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Cochrane fluoridation review. III: Misleading section on dental fluorosis Ken Perrott Jul 03

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The Cochrane review did not look at the effect of community water fluoridation (CWF) on dental fluorosis. It simply reviewed data on the prevalence of dental fluorosis at different fluoride drinking water concentrations – up to 7.6 ppm which is well outside the optimum concentration used for CWF.

This is strange for a review specifically about CWF. Strictly speaking, as it stands  this section should have been a separate review on dental fluorosis itself. However, this review did calculate a probable dental fluorosis prevalence at 0.7 ppm (the usual concentration used in CWF) which is misleading because it can be misinterpreted as due completely to CWF when it isn’t. And, of course, anti-fluoridation propagandists have cherry-picked and misinterpreted this.

The forms of dental fluorosis. Questionable, Very Mild and Mild forms are usually considered positively whereas the Moderate and Severe forms are considered negatively. See Water fluoridation and dental fluorosis – debunking some myths

Confusing language

I think is was a serious mistake for the reviewers to include this section in a review on CWF as this can imply the calculated prevalences quoted are caused by CWF. They aren’t.

Strictly, their calculations were reported correctly in the abstract:

“There is a significant association between dental fluorosis (of aesthetic concern or all levels of dental fluorosis) and fluoride level.”

And also in the Plain Language Summary:

“The researchers calculated that, in areas with a fluoride level of 0.7 ppm in the  water, approximately 12% of the people evaluated had fluorosis that could cause concern about their appearance.”

However, in their blog post on the review (see Little contemporary evidence to evaluate effectiveness of fluoride in the water”) they inappropriately claim:

“There is an association between fluoridated water and dental fluorosis.”

Quite wrong – the association was with fluoride concentration (and most studies were of natural fluoride levels) – not with CWF.

They also use the term “water fluoridation” incorrectly in their comment on other possible harm from fluoride:

“Five studies that reported on dental fluorosis also presented data on the association of water fluoridation with skeletal fluorosis (Chen 1993; Jolly 1971; Wang 2012), bone fracture (Alarcon-Herrera 2001), and skeletal maturity (Wenzel 1982), in participants between the ages of six and over 66 years. Four of the studies included a total of 596,410 participants (Alarcon-Herrera 2001; Chen 1993; Wang 2012; Wenzel 1982), and fluoride concentration in all four studies ranged from less than 0.2 ppm to 14 ppm.”

Their use of the term “water fluoridation” to cover natural fluoride concentrations up to 14 ppm is irresponsible and misleading.

What the review did on dental fluorosis

It simply attempted to find a quantitative relationship between “fluoride level” (concentrations of naturally derived fluoride in drinking water) and dental fluorosis prevalence. It did this for all grades of dental fluorosis from “questionable” to “severe” (see figure above for illustrations fo the different grades). It also did this for “dental fluorosis of aesthetic concern” (which they arbitrarily defined as the mild, moderate and severe forms – they acknowledge inclusion of “mild” forms here is debatable). The figure below gives an idea of the data they were working with.


Using this data they produced tables of the probability of any forms of dental fluorosis, and of dental fluorosis of aesthetic concern at fluoride concentrations from 0.1 to 4 ppm. In the figures below I have converted their probability values to a calculated prevalence of dental fluorosis at concentrations up to 0.7 ppm.


As you can see from these figures the calculated prevalence of dental fluorosis at “fluoride exposures” less than the 0.7 ppm is only slightly less that at the 0.7 ppm used in CWF. So  it is very misleading to interpret the review’s statement below as indicating anything about CWF:

“The researchers calculated that, in areas with a fluoride level of 0.7 ppm in the  water, approximately 12% of the people evaluated had fluorosis that could cause concern about their appearance.”

Why should the review have considered differences between fluoridated and unfluoridated areas for its conclusions about tooth decay – but ignore the differences between fluoridated and unfluoridated areas in its consideration of dental fluorosis?

Estimating possible effect of CWF on dental fluorosis

In Misrepresentation of the new Cochrane fluoridation review I estimated what the possible effects of CWF is from the calculated probabilities in the Cochrane review. I am surprised the reviewers do not do this themselves as their review was meant to be about CWF and not natural fluoride levels in general.

At 0.7 ppm (the usual concentration for CWF), the calculated prevalence of all forms of dental fluorosis is 40%. But to calculate the prevalence due to CWF we must subtract the prevalence for non-fluoridated water. So dental fluorosis due to CWF would be 40% – 33% = 7 % of people  (using the review’s concentration for non-fluoridated water of 0.4 ppm) or 40% – 30% = 10 % of people (using a more realistic concentration of 0.2 ppm).

Similarly, if we consider only those forms of dental fluorosis the review considers of “aesthetic concern,”  then calculated prevalence due to CWF amounts to only 12% – 10% = 2% of people (using the reviews definition of non-fluoridated) or 12% – 9% = 3%  of people using a more realistic concentration of 0.2 ppm for non-fluoridated.

Defining “dental fluorosis of aesthetic concern”

The milder forms of dental fluorosis are usually judged positive from the point of view of the quality of life. That is why the review also considered dental fluorosis of aesthetic concern – which they define as the severe, moderate and mild forms of dental fluorosis. But, their inclusion of mild forms here is questionable and they acknowledge that:

“Within the context of this review dental fluorosis is referred to as an ’adverse effect’. However, it should be acknowledged that moderate fluorosis may be considered an ’unwanted effect’ rather than an adverse effect. In addition, mild fluorosis may not even be considered an unwanted effect.”

It is not surprising (considering the data in the figures above) that surveys  usually find no changes in the severe and medium forms of dental fluorosis (usually considered of “aesthetic concern”) due to CWF.

I think the Cochrane reviewers were irresponsible to quote calculations which did not include the difference between fluoridated and non-fluoridated areas. This has enabled anti-fluoridation propagandists to use the authority of the Cochrane name to imply, as they often do, that CWF causes a dental fluorosis prevalence of 40%!


The review section on dental fluorosis should not be read as information on the effects of CWF – although the presented data can be used to calculate possible effects. These calculations confirm findings of published surveys that CWF has no effect of the forms of dental fluorosis of aesthetic concern.

However, the conclusions presented in this section of the review are open to misrepresentation and distortion just as they are with the reviews comments on “bias” and poor quality of research (see Cochrane fluoridation review. II: “Biased” and poor quality research) and their selection criteria (see Cochrane fluoridation review. I: Most research ignored). Misrepresentation and distortion of the review are already happening. Anti-fluoridation activists are heavily promoting this review, together with their distortions and misrepresentations, opportunistically using  the Cochrane name to give “authority.”

Sensible readers will not rely on such misrepresentation or brief media reports. Nor will they rely on the Abstract or Plain Language Summary – which have problems. They will read the whole document – critically and intelligently. This is the only way to find out what the true content of this review is.

See also:

Misrepresentation of the new Cochrane fluoridation review
Cochrane fluoridation review. I: Most research ignored
Cochrane fluoridation review. II: “Biased” and poor quality research

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June ’15 – NZ blogs sitemeter ranking Ken Perrott Jul 01

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Big problems with Sitemeter

The problems with SiteMeter are even worse this month. No data could be obtained for about 50 blogs using SiteMeter. People have also reported strange results. So if you wish to query the information in the table I suggest you check out the data in the SiteMeter pages.

If you are using SiteMeter, and especially if you find you page isn’t included this month, I suggest you consider transferring to a more reliable counter like StatCounter. Have a look at the NZ Blog Rankings FAQs if you need help with this.

There are now over 300 blogs on the list, although I am weeding out those which are no longer active or have removed public access to sitemeters. (Let me know if I weed out yours by mistake, or get your stats wrong).

Every month I get queries from people wanting their own blog included. I encourage and am happy to respond to queries but have prepared a list of frequently asked questions (FAQs) people can check out. Have a look at NZ Blog Rankings FAQ. This is particularly helpful to those wondering how to set up sitemeters. Please note, the system is automatic and relies on blogs having sitemeters which allow public access to the stats.

Here are the rankings of New Zealand blogs with publicly available statistics for June 2015. Ranking is by visit numbers. I have listed the blogs in the table below, together with monthly visits and page view numbers. Meanwhile I am still keen to hear of any other blogs with publicly available sitemeter or visitor stats that I have missed. Contact me if you know of any or wish help adding publicly available stats to your bog.

You can see data for previous months at Blog Ranks

Subscribe to NZ Blog Rankings Subscribe to NZ blog rankings by Email Find out how to get Subscription & email updates


Rank Blog Visits/month Page Views/month
1 Kiwiblog 1548697 3577649
2 Whale Oil 1330186 2800038
3 The Standard 238368 501340
4 The Daily Blog 174442 288345
5 No Right Turn 101646 532892
6 OracleNZ by Francisco Munoz Alvarez 61225 71566
7 Liberation 35155 191265
8 Sciblogs 34619 230987
9 Liturgy 21606 34118
10 No Minister 17655 23198
11 Mama said 17347 19403
12 Offsetting Behaviour 17023 135928
13 Homepaddock 11548 16165
14 Tikorangi: The Jury Garden 11285 13919
15 Music of sound 11230 120521
16 Fields of Blood 11164 16297
17 13th Floor 10863 16230
18 Bill Bennett 10177 56629
19 Nom Nom Panda 9677 12332
20 Keith Johnson Wellington NZ 8725 8839
21 Cycling in Christchurch 7879 10755
22 Talking Auckland 7851 10577
23 The Bloke 7706 12072
24 Open Parachute 7360 10027
25 Hot Topic 7084 9218
26 Right Reason 5877 7632
27 In the back of the net 5517 7941
28 Save our Schools NZ 5296 6184
29 Aotearoa: A wider perspective 5149 6412
30 Lindsay Mitchell 4012 21252
31 Anglican down under 3971 5155
32 Otagosh 3948 53151
33 Autism & Oughtisms 3813 3933
34 Reading the maps 3301 4606
35 Vomkrieg 3281 5160
36 MandM 3122 3802
37 Matte Shot 2974 4382
38 Home education Foundation 2840 4103
39 The Woolshed Wargamer 2759 5280
40 Scepticon 2758 24145
41 Chris no-frills 2688 14051
42 Quote Unquote 2620 2929
43 TVHE 2566 2710
44 Infectious thoughts 2419 6060
45 Rodney’s Aviation Ramblings 2251 2814
46 Off the couch 2203 3020
47 Woodleigh Nursery 2099 4802
48 Open Parachute @ SciBlogs 1969 2241
49 Kiwi Cakes 1961 2656
50 New Zealand Conservative 1866 2280
51 misc.ience @ Sciblogs 1828 11434
52 Blessed Economist 1606 16726
53 Waiology 1590 10520
53 AmeriNZ 1590 2004
55 Canterbury Atheists 1534 15545
56 PM of NZ 1506 17058
57 Super Rugby Tips 1473 1804
58 Helen Heath 1370 1713
59 Eye on the ICR 1273 1523
60 Dark Brightness 1265 2120
61 Man of Errors 1218 1356
62 Derek’s blog 1212 7966
63 Windy Hilltops 1198 6412
64 Put ’em all on an island 1150 1433
65 james lin’s blog 1128 1199
66 Cambridge NZ 1091 1929
67 Pdubyah –  a life just as ordinary 1061 1916
67 Sugar’s the new Durries 1061 1916
69 Life Behind the IRon Drape 1040 2180
70 Stratford Aerodrome 1035 1356
71 Undeniably Atheist 1001 1139
72 Wysiwygpurple’s Blog 905 1427
73 Life is not a race to be finished first 886 11888
74 Michael Jeans 875 1291
75 ICT Teaching and Learning 874 1408
76 713 1024
77 The IT Countrey Justice 676 896
78 Show your workings 665 9579
79 Social Media & the 2014 Election 661 798
80 Socialist Aotearoa 653 731
81 Anne Free Spirit 630 930
82 Keeping Stock 591 702
83 Four seasons in one 584 700
84 Room One @ Auroa School 570 1860
85 Tararua District Library 513 3307
86 Keeping stock 487 3812
87 One Furious Llama 486 2837
88 Polit Ecol 466 550
89 Kidney Punch  448 494
90 Ideologically impure 432 476
91 Stitchbird 431 2667
92 Media Sport and Other Rantings 427 517
93 Perissodactyla 421 486
93 Quietly in the backgroud 421 486
95 Einstein Music Journal 416 515
96 Brennan McDonald 412 451
97 Exile in New zealand 411 647
98 In a strange land 387 6034
99 goNZo Freakpower Brains Trust 369 380
100 Room 5 @ Melville Intermediate School 360 450
101 sticK 349 412
102 My thinks 337 378
103 Get Out Gertrude! 312 464
104 Capitalism is bad 306 3906
104 ElephaNZa  306 315
106 Family integrity 304 317
107 Tauranga Blog 301 331
108 Creative Voice# 300 780
109 Glenview 9 295 313
109 SmallTorque 295 327
111 Dad4justice 266 288
112 Spatula Forum 260 4806
113 Skeptiocon @ Sciblogs 259 2888
114 roarprawn 244 5623
115 Software development and stuff 242 251
116 Glennis’s Blog Page# 240 360
117 Hitting Metal With A Hammer 235 4383
118 Unity Blog 231 239
119 jontynz 206 301
120 203 234
121 Wokarella 202 283
122 The Fundy Post 194 2600
122 Lost Soul 194 206
124 MartinIsti Blog 184 280
125 Manaia Kindergarten 180 420
126 Kutarere’s Blog  178 1877
127 Spratts 167 365
128 Samuel Dennis 165 178
129 Toni Twiss 160 162
130 Nelsonian’s life 150 210
130 AnneKcam
150 300
130 King’s High School Library 150 300
133 $100 Dialysis 141 162
134 Sacreparental 139 169
135 The Little Waaagh! That Could 135 163
136 kiwi simplexity 132 143
137 Upstage 127 252
138 Mountains of Our Minds# 120 150
139 High voltage learning during the Christchurch earthquakes 118 159
140 Fuller’s watch 114 139
141 Dragonsinger 113 4525
142 Canvassing for opinion 105 1188
143 Prior Knowledge  104 357
143 Carolyn’s blog 104 130
145 Creative Collision 103 103
145 This Mum Rocks 103 219
147 New Zealand Indian Fine Arts Society 97 126
147 Sharlene says 97 122
149 NZ First Youth 93 366
150 The Well read Kitty 92 98
151 Digital learning 90 90
151 Virtual North 90 120
153 Cut your hair 83 84
154 Grumpollie 72 99
155 John Macilree’s Blog 70 76
156 jo russ photo diary 64 3243
156 Episto 64 64
156 Social Policy Bonds Blog 64 93
159 You’re Underthinking 61 164
159 University of Otago, Law Library Blog 61 79
161 The Catalyst 60 60
161 Pt England Scribes 60 60
161 Korero Pt England 60 120
164 Ellie Great 56 70
165 ah! New Year’s Resolution 54 73
165 Journey to a mini me 54 87
167 New Zealand female Firefighter calendar 51 52
168 UpsideBackwards 50 692
169 Write to travel 49 175
169 KJT 49 64
171 Looking in the square 42 446
172 Politicalisation 39 89
173 Whitireia Journalism School 36 40
174 SageNZ 30 268
174 John Macilree’s Weblog# 30 60
174 Room 24, 2012 30 60
174 James McKerrow – Surveyor 1834-1919# 30 60
174 The Official Ebenezer Teichelmann Blog# 30 60
174 ICTPD 30 30
174 Sleeping with books 30 60
174 Kiwi Chronicles 30 30
174 Making IT Happen 30 60
174 But Now 30 30
174 Football Tragic NZ 30 30
174 Anticipating future impacts 30 30
174 Moving the crowd 30 30
187 Oracle of Okarito 29 132
188 Busy Peas 28 429
189 Palmerston North.ifo 26 3084
189 The First Fifteen @ TIS 26 38
191 Frontlawn 18 310
192 Tertius 16 40
193 TimG_Oz Blog 15 22
194 Tangled up in purple 13 99
194 A communist at large 13 26
196 ZL2UCX’s Blog 12 12
197 Nathanael Baker 11 309
197 SilverSpikes Photography  11 13
199 Shelly van Soest Artist 10 10
200 The Secret Life of Russ  8 467
201 kiwiincanberra 7 7
202 Liminal Spaces 6 6
202 Rambling Reflections 6 6
204 Auckland Transport Blog 5 6
205 The REAL Steve Gray 3 184
205 Bob McKerrow – Wayfarer 3 3
207 ObservatioNZ 2 2
207 TraLIS blog 2 2
207 amiria [blog] 2 6
207 Moderation Blog 2 2
207 On the Left 2 2
207 Robtuckerpix’s Blog  2 2
207 ROI Marketing 2 2
207 Unknown Future 2 2
215 Here I stand 1 2
215 Teaching the Teacher 1 1
215 Roger Nome’s progressive Politics 1 1

Cochrane fluoridation review. II: “Biased” and poor quality research? Ken Perrott Jun 30

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Here again, the language used in the Cochrane review (Water fluoridation for the prevention of dental caries) is very misleading. Especially when cherry-picked and taken out of context. The word “bias” used in the review does not have the meaning an uninformed reader might think.

It does not mean motivated experimental design or selection of data to “prove” a predetermined outcome. Rather it has specific meaning related to common (and usually innocent) problems encountered clinical drug trials. These problems also occur in real-life epidemiological studies and trials of the sort used for evaluating social health measures like community water fluoridation (CWF) but the lack of control in such studies means they are harder to combat.. The Cochrane ideal of randomised double-blinded trials is just not realistic in these situations. As the American Academy of Pediatrics comments in their article on the Cochrane review:

“it would be a logistical nightmare to try creating a public water system that pumps fluoridated water to the first house on the block, delivers non-fluoridated water to the following two houses and then provides fluoridated water to the 4th and final house on that block.”

The review describes the types of “biases”  considered:

“Assessment of risk of bias in included studies
. . . . . The domains assessed for each included study included: sampling, confounding, blinding of outcome assessment, completeness of outcome data, risk of selective outcome reporting and risk of other potential sources of bias. . . . . .  We had identified the following factors as important confounders for the primary and secondary outcomes: sugar consumption/dietary habits, SES, ethnicity and the use of other fluoride sources.”

Unfortunately, all these sorts of “biases” are inevitable to some extent in the real world. Researchers do not always have the budget to include consideration of all confounders, or the degree of control required. There are inevitable gaps in data when families move or withdraw children from schools. Yet it is real-world studies, not idealised laboratory experiments, that give the data and other evidence reviewers and decision-makers must consider. Humans can’t be treated like experimental rats.

What “biases” did the review find

As far as “caries outcome” is concerned the review reports a  “high risk of bias overall,” but this “bias may occur in either direction.” This indicates there is not a motivated selection of data or experimental design to produce a predetermined result as that would show up as a systematic bias.

The major cause of “bias” arose from lack of control of the confounding issues of “sugar consumption/dietary habits, SES, ethnicity and the use of other fluoride
sources.” These are of course important factors which could influence results. In the real world it is difficult to control of variations in dietary intake, although socioeconomic status (SES) and ethnicity can be included in statistical analyses of data. My impression is that this is usually done in more recent studies (which the Cochrane review team had excluded from their review – see Cochrane fluoridation review. I: Most research ignored).

Most studies were at low risk of “bias” from sampling methods but on “detection bias” the reviewers report:

The majority of the studies did not blind outcome assessors. This is perhaps unsurprising when considering the efforts that may be required to blind assessors for this type of study.”

The qualification here surely indicates the inadequacy of the Cochrane criteria for using word’s like “bias” which are more fitted to clinical drug trials than evaluation of social health policies.

Most studies did not suffer from “incomplete outcome data” where some data is not measured, but some showed the “bias” of “selective reporting” where data sets reported were incomplete. Interestingly the reviewers report one study where:

“the baseline fluoridation status of the children was determined by the location of the school they attended, which may not have taken into account any children attending schools in fluoridated areas who resided outside those areas.”

This must be a common problem researchers face when they do such real-world epidemiological studies.

Inappropriate criteria used to judge quality of research

Given the nature of evaluating a social health policy like community water fluoridation (CWF) I think the criteria used by the review team to judge the quality fo available research was quite wrong. Their criteria were more fitted to judging clinical drug trials and not social health policies. They acknowledge this in their discussion section “Quality of evidence:”

“However, there has been much debate around the appropriateness of GRADE when applied to public health interventions, particularly for research questions where evidence from randomised controlled trials is never going to be available due to the unfeasibility of conducting such trials. Community water fluoridation is one such area.”


“we accept that the terminology of ’low quality’ for evidence may appear too judgmental. We acknowledge that studies on water fluoridation, as for many public health interventions, are complex to undertake and that researchers are often constrained in their study design by practical considerations. For many public health interventions, the GRADE framework will always result in a rating of low or very low quality. Decision makers need to recognise that for some areas of research, the quality of the evidence will never be ’high’ and that, as for any intervention, the recommendation for its use depends not just upon the quality of the evidence but also on factors such as acceptability and cost-effectiveness (Burford 2012).” My emphasis.

These are important qualifications which, however, did not make it into the review’s Abstract or Plain Language Summary – and certainly not into media reporting. I think the review team was irresponsible to omit such qualifications from their summaries – and many people might suggest they were irresponsible to use such inappropriate criteria for their judgements in the first place.

The scientific literature is not perfect

I keep stressing that readers should always approach scientific reports and papers critically and intelligently. The problems identified by the Cochrane reviewers are inevitable and should always be taken into account by sensible readers. Simple reliance on the abstract of a paper or report often gives a misleading interpretation of the findings. Unfortunately, even unmotivated reporters tend not to read reports in full. Motivated activists will purposely resort to cherry-picking and distortion.

Decision-makers don’t necessarily need perfect scientific papers as they have to consider far more than the abstract conclusion of a scientific paper. There are the democratically expressed views of the electorate and the real situation where social health policies are put into effect. While the Cochrane reviewers expressed “limited confidence” in the size of the effect of CWF on tooth decay. However, policy-makers are more interested in the fact that there is a positive effect on oral health than the possible “theoretical” size of that effect.After all, policy-makers have to also consider the possible role of confounding effects like alternative sources of fluoride, the quality of dental health in the area, socioeconomic status of the population and school health programmes when making decisions about local CWF programmes.


1: The Cochrane reviewers’ use of terms like “bias” and judgment of studies as being of poor quality is inappropriate for evaluation of a social health policy. According to them:

“The main areas of concern were confounding and lack of blind outcome assessment. The evidence was additionally downgraded for indirectness due to the fact that about 71% of the caries studies that evaluated the initiation of water fluoridation were conducted prior to 1975.”

Yet they qualify this by acknowledging such judgement of “bias” and poor quality is inappropriate for a social health policy. And it was their own criteria for rejecting studies that produced a paucity of more recent studies (see Cochrane fluoridation review. I: Most research ignored).

2: These qualifications were not mentioned in the review’s Abstract or Plain Language Summary. I believe this was irresponsible of the authors. especially  given the controversial nature of the subject and the well-understood fact that media reporters rarely read beyond abstracts and summaries.

Such inappropriate and unqualified language provides a godsend to anti-fluoridation propagandists who are already cherry-picking and misrepresenting the review’s main findings.

3: We can remove the inappropriate and judgmental language and still accept that many of the problems identified in the review are inevitable for studies of social health measures. The review actually acknowledges that.

However, the sensible reader of scientific literature is surely aware of these problems. Any research paper must be assessed intelligently and critically – especially regarding the treatment of confounding factors. This is a point I have continually stressed in my posts on this subject.

In my experience, it has been the confirmation bias of anti-fluoride activists which leads them to ignoring such advice. One need only consider their use of studies related to IQ and fluoride in areas of endemic fluorosis, or their recent promotion of poor quality papers claiming a relationship between CWF and Attention-Deficit Hyperactivity Disorder (see ADHD linked to elevation not fluoridation) or hypothyroidism (see Paper claiming water fluoridation linked to hypothyroidism slammed by experts). 

I urge readers to follow this same advice with the Cochrane review. Don’t accept media reports or a limited reading of its Abstract or Plain Language Summary.

Read the whole review – intelligently and sceptically.
See also:

Cochrane fluoridation review. I: Most research ignored

Similar articles

Cochrane fluoridation review. I: Most research ignored Ken Perrott Jun 29


With the publication of the new Cochrane Fluoridation Review (Water fluoridation for the prevention of dental caries) we have, once again,  both fluoridation supporters and opponents claiming it as evidence for their contradictory positions. They surely both cannot be right.

The reality is that any such review is going to have its own complexities and limitations which allow committed believers on either side to confirm their biases. Unfortunately, this confirmation bias is promoted by inadequate reporting relying on “sound bites” from the executive summary.  Real understanding of the review and its results requires more thoughtful analysis, a reading of the full review and not just media reports and a bit of thinking about its limitations.

The post is the first of three articles looking a bit more deeply at the Cochrane fluoridation review. Here I discuss the strict criteria used by the review team for selecting the studies they considered,  the limitations this has caused for their findings and the misinterpretation of the review results this has produced.

97% of fluoridation research ignored

This seems amazing – why ignore so much of the research? We can understand the need to filter poor research or poorly reported claims. But 97%?

Yet, that is what the review reports – and summarises in their Figure 1:


The high exclusion rate was caused by the review teams decision to only consider studies which conformed to strict criteria:

“For caries data, we included only prospective studies with a concurrent control, comparing at least two populations, one receiving fluoridated water and the other non-fluoridated water, with at least two points in time evaluated. Groups had to be comparable in terms of fluoridated water at baseline. For studies assessing the initiation of water fluoridation the groups had to be from nonfluoridated areas at baseline, with one group subsequently having fluoride added to the water. For studies assessing the cessation of water fluoridation, groups had to be from fluoridated areas at baseline, with one group subsequently having fluoride removed from the water.
For the purposes of this review, water with a fluoride concentration of 0.4 parts per million (ppm) or less (arbitrary cut-off defined a priori) was classified as non-fluoridated.”

This criteria requiring measurements at several time periods and the inclusion of data from before the commencement of fluoridation was probably the main reason for excluding studies. In the review’s Table “Characteristics of excluded studies” the most often mentioned reason was “Evaluated caries in a single time point cross-sectional study.”

OK, you can sort of see the logic behind these strict criteria:

“The cross-sectional studies, whilst able to provide information on whether water fluoridation is associated with a reduction in disparities, are not able to address the question of whether water fluoridation results in a reduction in disparities in caries levels.”

But this inevitably resulted on consideration of only a small part of the available research:

“155 studies (162 publications) met the inclusion criteria for the review. However, only 107 studies (15 caries studies; 92 studies reporting data on either all fluorosis severities or fluorosis of aesthetic concern) presented sufficient data for inclusion in the quantitative syntheses.”

Inability to comment does not mean no effect

Exclusion of so many important studies meant the review was unable to come to any conclusions about important aspects like the effect of community water fluoridation (CWF) on socioeconomic difference in tooth decay,  the effect of stopping CWF programmes on later tooth decay and the effectiveness of CWF in reducing adult tooth decay.   Yet, in the review’s discussion they did make note of research which did draw some conclusions in these areas – research they refused to consider. (And it is rather ironic that one of the review’s authors, Helen V. Worthington, has co-authored several papers which conclude that CWF does reduce socioeconomic differences in dental health).

Of course, anti-fluoride propagandists have chosen to misrepresent the review – reporting its inability to draw conclusion on these questions as evidence that CWF does not influence socioeconomic differences, is not effective for adults and tooth decay does not increase when CWF is stopped!  (See Misrepresentation of the new Cochrane fluoridation review). Clear misrepresentation – but helped by the combination of exclusion of most research and the  vague language used in the review summary.

And you do sort of wonder at ignoring so much evidence when considering issues related to community health. Was Cochrane throwing away the baby with the bathwater?

Confirmation fluoridation is effective

The strict exclusion criteria enabled the review team to winnow studies down to a small number which could be analysed quantitatively. They were able to confirm from analysis of 9 studies that CWF:

“resulted in a 35% reduction in decayed, missing or filled baby teeth, and 26% reduction in decayed, missing and filled permanent teeth.”

But the strict exclusion criteria, specifically rejection of cross-sectional studies, is still a fly in the ointment. Recent studies of situations where fluoridation has been in operation for a long time did not fall within the strict selection criteria because pre-fluoridation data would not realistically be available in most cases. The review consequently did not consider properly the recent evidence – 71% of the research considered occurred before 1975!

The review, therefore, raised the issue of how applicable their findings are to the current situation in developed countries because of improved dental care and use of fluoridated toothpaste. A reasonable proviso which could have been discussed properly using the research they had excluded. But again a proviso which enables misrepresentation by anti-fluoride propagandists who imply that their findings are irrelevant to our current situation.

The review authors acknowledge that exclusion of such data presents a problem for their conclusions:

“In the past 20 years, the majority of research evaluating the effectiveness of water fluoridation for the prevention of dental caries has been undertaken using cross-sectional studies with concurrent control, with improved statistical handling of confounding factors (Rugg-Gunn 2012). We acknowledge that there may be concerns regarding the exclusion of these studies from the current review. A previous review of these cross-sectional studies has shown a smaller measured effect in studies post-1990 than was seen in earlier studies, although the effect remains significant. It is suggested that this reduction in size of effect may be due to the diffusion effect (Rugg-Gunn 2012); this is likely to only occur in areas where a high proportion of the population already receive fluoridated water.”

Of course, the review team was correct to raise the question of the possible reduced efficacy of CWF in modern developed societies. But doesn’t that suggest they should not have used such restrictive criteria in selecting studies to consider? And isn’t it irresponsible to leave the impression that CWF is no longer effective when they excluded the studies which could have provided better answers?


The Cochrane fluoridation review suffers from the fact that only 3% of available studies were considered. The restrictive selection criteria enable quantitative estimates showing  CWF is effective for children but excluded the possibility of answering questions related to the effectiveness for adults, the ability of CWF to reduce socioeconomic differences in oral health,  the effect of stopping fluoridation on later tooth decay and whether improved availability of dental treatments and use of fluoridated toothpaste has reduced the efficacy of CWF in modern developed societies.

The language of the review report itself encourages misinterpretation – and this is even worse in their blog post about the review – Little contemporary evidence to evaluate effectiveness of fluoride in the water.” Here they repeatedly refer to lack of evidence but only explain this is due to their exclusion of such evidence in a few places. What is the uninformed reader, who does not bother to read the full document, make of points in the summary such as:

  • “There is insufficient evidence to determine the effect of water fluoridation on disparities in caries levels across socio-economic status
  • There is insufficient evidence to determine the effect of water fluoridation on caries levels in adults
  • There is insufficient evidence to determine the effect of removing water fluoridation programmes from areas where they already exist”

Finally, anti-fluoride propagandists are motivated enough to misrepresent the findings in any fluoridation review or other documents. The very restricted selection criteria used by the Cochrane review and the language of its summary and news reporting of the review is a bit of a godsend to such propagandists.

Expect to see a lot of cherry-picked quotes from the Cochrane review. Twisted to turn the lack of evidence of effects (due to the exclusion of studies) into evidence for no effect.

My next article on the Cochrane review will deal with its discussion of “bias” and poor quality in the studies it considered.

See also:

Misrepresentation of the new Cochrane fluoridation review

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What is causing warming of the earth? Ken Perrott Jun 28


Bloomberg has a great article showing why climate change deniers have it all wrong when they argue that the observed global warming is explained by natural causes. It just isn’t. The article is What’s Really Warming the World? Climate deniers blame natural factors; NASA data proves otherwise.

Here are the main points and graphics which compare the observed changes in earth’s temperature  with the changes expected from individual factors:

Natural factors

Changes in the earth’s orbit around the sun (blue line) have had a negligible effect on warming:


Changes in the sun’s temperature (orange line)have also had a negligible effect:


Volcanos influence the earth’s temperature, usually causing decreases,(red line) but cannot explain the observed warming:


Natural factors combined (earth’s orbit, sun temperature and volcanoes) (green line) cannot explain the observed warming:


Human factors

Changes in land use, like deforestation, (light green line) actually have a cooling effect:


Ozone level changes (light blue line) have only a slight warming effect:


Aerosol pollution (purple line) has had a marked cooling effect:


Greenhouse gas concentration increases (green line) have had a marked warming effect – it is clearly the main factor responsible for global warming:


When all the human factors, ozone, land use, aerosols and greenhouse gases, are combined the models (blue line) show a good agreement with observed temperature changes (black line):


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New science bloggers wanted for Sciblogs 2.0 Ken Perrott Jun 26

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Sciblogs 2.0 coming soon

After nearly six years in operation, Australasia’s largest blog network is getting a facelift and some fresh voices.

Sciblogs features commentary from around 30 scientists and science writers and is consistently ranked among the country’s top 10 blogs based on Sitemeter statistics.

But the platform is well overdue for a revamp and will soon be relaunched with a new look, new additions to the blogging line-up and a remit of appealing to a wider audience.

Among the changes will be:

  • A more visual look and refreshed blog homepages
  • Mobile-friendly design so Sciblogs looks good on smartphones and tablets
  • Some new bloggers covering everything from drones to psychology
  • News content drawing from sources such as our new research news portal.

Become a Scibling

We are on the lookout for new science bloggers to join our lively stable of bloggers and as well as writers, videographers and social media gurus who are passionate about science communication and who are keen to collaborate on Sciblogs.

“The likes of Iflscience, Science Alert and the science blog networks of Scientific American and Scienceblogs shows there’s strong appetite for science news and commentary,” said Sciblogs editor and SMC Director, Peter Griffin.

“We want to grow the Sciblogs community featuring the best, most interesting science from New Zealand and around the world. We’ll improve our mobile and social media presence so Sciblogs content is easier to browse and share.”

The new Sciblogs will go live by the end of August – contact if you would like to get involved.

Gagging of scientists – a common problem? Ken Perrott Jun 25

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A recent NZ Association of Scientists survey indicates that 40% of NZ scientists report they feel gagged from communicating their scientific findings to the public. Management policies and funding problems were blamed and there are issues around “embarrassing the government.”

The Science and Innovation Minister, Stephen Joyce, is not convinced by the survey results but is unwilling to accept there is a problem without  “a heck of a lot more evidence than we’ve got from one write-in survey.” (See Call for closer look at scientists’ claims | Radio New Zealand News.)  You can be sure he won’t go out of his way to look for such evidence.

Wider than direct censorship

Despite Joyce’s attempts to “turn a blind eye,” I think there is a problem and can certainly remember examples from my time working in a Crown Research Institute (these problems may not be as bad in the Universities). But the problem is wider than direct censorship – limiting publication because of commercial sensitivity, protection of intellectual property,  fear of scaring away or offending potential funders and succumbing to legal action – or just threats of legal action – from commercial interests.

There is also the gagging effect arising from the institutional culture, the attitudes and perceived interests of management bureaucracy, the old-boy network (which these days incorporates people from the commercial  sectors as well as the government and political system). I experienced an example of the old-boy network when a National MP attempted to get my director to “discipline” me because I had made a public statement on nuclear disarmament! I am sure this sort of “behind the scenes” pressure is exerted all the time on research institute managements by commercial and political figures. And how often do management figures consider the interests of freedom of expression and information, or the responsibility of science to communicate with the public, when subjected to such pressure with its implied threats to the funding or “name” of the institute?  Or to the career of the management figure themselves?

Wider than one’s own research

The issues, for and against, may be fairly clear when the findings being gagged are the research results of the scientists themselves. But scientists do have the responsibility to speak up about science itself, and about general findings which may not be directly linked to the narrow field of specialisation of the scientist concerned.

This is especially true today when so much pseudoscience and outright distortion of science is promoted in the public sphere. Very often the promotion is done in the interests of business so managements may feel the need to prevent staff from fulfilling such responsibilities so as to avoid commercial pressures on the institute.

A common example is the scientific misinformation peddled by the “natural”/alternative health industry, which today is a big and profitable business – despite attempting to present itself as the “David” challenging the “Goliath” of “Big Pharma.”

Institutional management may pressure staff not to face up to their responsibility to fight this misinformation – especially if they believe there may be possibilities of research contracts from businesses within that industry. Maybe management will express this in relatively bland terms such as the need to protect the “name” and “reputation” of the institute. Or express the concept that the institute should not be seen to be “taking sides” as this undermines its credibility and appearance of objectivity.

Becoming a “street fighter” or abdicating scientific responsibility?

Then, of course, there is just the outright viciousness of some anti-science campaigners. Getting into public fights with some ideologically motivated activists can be like participating in a pub brawl. Responsible management cannot be happy about staff being seen as “street fighters.”

Management also has a responsibility not to expose their staff to danger. In New Zealand District Health Boards have tended not to take part in public meetings which are stacked with anti-fluoride activists – partly for the safety reason. And recent reports of attacks on health spokespersons and city council leaders, by anti-fluoride activists, show this is a reasonable concern (see  Lismore mayor assaulted in broad daylight by fluoride-hater, and Beware the violent antis – Lismore Mayor physically assaulted).

33618It is a complex issue. On the one hand engagement with those who are misrepresenting science can sometimes end up like fighting a pig – one’s opponent is so slimy they can escape from any rational debate and the expert ends up just a dirty as the pig in the end. In the other hand not to take part in the public debate  results in the abdication of our scientific responsibilities and handing over the public issue to those who promote misinformation and pseudoscience. (In NZ anti-fluoride propagandists are continually claiming  the refusal of district health boards to front up to their meetings as evidence that science does not support fluoridation!)

Social media

Social media can be just as nasty to pro-science people who attempt to challenge misrepresentation and pseudoscience (have a look at the abuse rendered by the Australian anti-fluoride propagandist Dan Germouse here). There is little point in engaging extremists on social media – unless one is sure there are other readers, or “lurkers,” who may learn something from the exchange.

But one thing is sure, advocates of science do not use social media as often or as effectively as they should. Studies do show that pseudoscientific groups and those peddling scientific misinformation tend to dominate social media like Facebook and Twitter. Social media can be effective in creating opinions – and anyway it is a popular forum which we ignore at our peril.  Scientists need to find ways to effectively take part in social media – if we don’t we are abdicating our responsibility to society to defend science and oppose misinformation.


Gagging of scientists is much wider than the few cases where publication of individual research findings is restricted.Unfortunately institutional culture, its conservatism, authoritarianism and bureaucracy, inhibit the freedom of scientists to take part in the public debate around scientific issues. They inhibit participation in social media where much of the public debate occurs (see Science and social media in new Zealand). Institutional culture can therefore restrict a scientist’s ability to fulfill his or her responsibility to communicate science to the public and to oppose widespread misinformation and pseudoscience.

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I wish more people were aware of this Ken Perrott Jun 22

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Misrepresentation of the new Cochrane fluoridation review Ken Perrott Jun 20

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A new fluoridation review was published this week – Water fluoridation for the prevention of dental caries from the Cochrane Oral Health Group. It’s main message is:

“Data suggest that the introduction of water fluoridation resulted in a 35% reduction in decayed, missing or filled baby teeth and a 26% reduction in decayed, missing or filled permanent teeth. It also increased the percentage of children with no decay by 15%. These results indicate that water fluoridation is effective at reducing levels of tooth decay in both children’s baby and permanent teeth.”

So, of course, we now have to put up with anti-fluoridation propagandists as they scurry to misrepresent the review’s findings.

I have written before about how Stan Litras, a New Zealand anti-fluoride propagandist,  indulges in cherry-picking, misinformation and outright distortion  of the science (see for example  Cherry-picking and misinformation in Stan Litras’s anti-fluoride article). Well, he has been at it again – this time putting his talents for misrepresentation to use on the new Cochrane Review.

Stan has issued a press release, using his astroturf vanity project (Fluoridation Network for Dentists) – Gold Standard Fluoride Review Contradicts NZ Advice. He claims that the new review’s:

“findings are completely at odds with last year’s Royal Society review, which our government refers to as justification for promoting fluoridation.”

In fact just not true!

Let’s compare his claims with what the Cochrane review actually reported.

Adult benefits

Stan claims the review “finds the science does not support claims that water fluoridation is of any benefit to adults.” Of course, Stan is implying that the review investigated the situation for adults and found no benefit.

Completely wrong.

The review says:

“No studies met the review’s inclusion criteria that investigated the effectiveness of water fluoridation for preventing tooth decay in adults, rather than children.”

And later:

“Only one of these studies examined the effect of water fluoridation on adults (Pot 1974); the reported outcome for this study was the percentage of participants with dentures. There are no data to determine the effect of water fluoridation on caries levels in adults.”

The Cochrane reviewers just did not have any suitable studies fitting their strict criteria for analysis so they could draw no conclusion on this specific question. However, in the review’s discussion they do mention a comprehensive systematic review (Griffin et al., 2007) which attributed a 34.6% reduction of tooth decay in adults to community water fluoridation. The corresponding figure for studies published after 1970 was 27.2%

Social inequalities

Stan implies the review found that fluoridation did not “reduce social” inequalities.

Completely wrong again.

The review was not able to draw any conclusion related to social inequalities because it just did not have that information. it says:

“There was insufficient information available to find out whether the introduction of a water fluoridation programme changed existing differences in tooth decay across socioeconomic groups.”

The review team did find 3 studies reporting effects of water fluoridation on disparities in caries across social class. However, there were problems with all 3 studies meaning the data was not suitable for further analysis and this  prevented them drawing any conclusions.

Benefits when toothpaste used

Stan claims, or at least strongly implies,  the review indicates that community water fluoridation does not “provide additional benefits over and above topically applied fluoride (such as in toothpaste).”

Again, completely wrong.

The review specifically says:

“Data suggest that the introduction of water fluoridation resulted in a 35% reduction in decayed, missing or filled baby teeth and a 26% reduction in decayed, missing or filled permanent teeth. It also increased the percentage of children with no decay by 15%. These results indicate that water fluoridation is effective at reducing levels of tooth decay in both children’s baby and permanent teeth.”

It goes on to say:

“However, since 1975 the use of toothpastes with fluoride and other preventive measures such as fluoride varnish have become widespread in many
communities around the world. The applicability of the results to current lifestyles is unclear.”

So, it raises the possibility that the current efficacy of community water fluoridation in industrialised countries could be lower. However, they could not draw a conclusion on this because only 30% of the included studies took place after 1975.

The review team did attempt to look at factors such as sources of fluoride “(potential confounders of relevance to this review include sugar consumption/dietary habits, SES, ethnicity and the use of other fluoride sources)” but found this not to be possible:

“However, due to the small number of studies and lack of clarity in the reporting within the caries studies, we did not undertake these sub-group analyses.”

Stopping fluoridation

Stan claims (or at least strongly implies) the review shows claims “that tooth decay increases in communities when fluoridation is stopped” are incorrect.

Wrong again.

The review says:

“There was insufficient information available to understand the effect of stopping water fluoridation programmes on tooth decay.”


“No studies that met the inclusion criteria reported on change in dmft or proportion of caries-free children (deciduous/permanent dentition) following the cessation of water fluoridation.”

The only study the review discussed was that of Maupome et al., (2001). This paper is often quoted by anti-fluoridation propagandists but those authors themselves commented on the difficulty of drawing conclusions from their data:

“Our results suggest a complicated pattern of disease following cessation of fluoridation. Multiple sources of fluoride besides water fluoridation have made it more difficult to detect changes in the epidemiological profile of a population with generally low caries experience, and living in an affluent setting with widely accessible dental services.”

Dental fluorosis

Stan claims the review “found that 40% of children in fluoridated areas have dental fluorosis.” However, the review does not compare the incidence of dental fluorosis in fluoridated areas and unfluoridated areas. It simply draws conclusions about the likely incidence of dental fluorosis at different fluoride intakes. This lack of comparison is unfortunate, although the omission may be due to the lack of suitable studies that survived their strict criteria.

So Stan’s claim is misleading because without considering dental fluorosis in the non-fluoridated areas it is not possible to attribute any responsibility to community water fluoridation. He has simply taken the reported estimate for a fluoride intake of 0.7 ppm (the concentration in fluoridated drinking water in NZ) without taking into account the occurrence of dental fluorosis in unfluoridated areas. Very misleading!

The review does, however, compare rates of dental fluorosis for different drinking water concentrations and we can draw some proper conclusions from these.

Total dental fluorosis. The review defines this as all the forms of dental fluorosis according to the Dean Index – from questionable to serious. (See Water fluoridation and dental fluorosis – debunking some myths for a discussion of the different forms of dental fluorosis). The graph below shows the reviews findings for the effect of fluoride exposure (drinking water fluoride concentration) on any dental fluorosis.

DF-2True, at 0.7 ppm (the usual concentration for CWF, this shows an incidence of 40%. But we can estimate the increase due to CWF by subtracting the incidence for non-fluoridated water. So the increase due to CWF would be 7% (using the review’s concentration for non-fluoridated water of 0.4 ppm) or 10% using a more realistic concentration of 0.2 ppm.

So Stan is quite wrong to imply CWF causes a total dental fluorosis increase of 40% – it is only 10% or less. However, even that figure is misleading.

Most dental fluorosis is not of aesthetic concern – in fact, the milder forms are often viewed positively from the point of view of the quality of life. So the review also considers dental fluorosis of aesthetic concern – which they define as the serious, moderate and mild forms of dental fluorosis (their inclusion of mild forms here is questionable). The graph below illustrates their findings for these forms of dental fluorosis.

So, if we consider only those forms of dental fluorosis the review considers of aesthetic concern  then increases due to CWF amount to only 2% (using the reviews definition of non-fluoridated) or 3% using a more realistic concentration of 0.2 ppm for non-fluoridated.

This is a huge difference to the 40% claimed by Stan.

The review acknowledges that their inclusion of mild forms of dental fluorosis in their definition of dental fluorosis of aesthetic concern is questionable, saying “mild fluorosis may not even be considered an unwanted effect.” Most studies do not consider the mild forms undesirable. It is likely that most of the increase in “dental fluorosis of aesthetic concern” arising from community water fluoridation occurs in the mild forms.  So my suggestion of a 2 or 3% increase in “dental fluorosis of aesthetic concern” will be an overestimation.

It is unsurprising, then, that some cross-sectional studies do not detect any increase in undesirable dental fluorosis attributed to community water fluoridation. The figure below illustrates an example reported in the New Zealand in the 2009 New Zealand Oral health Survey (see Our Oral Health).


Once again this anti-fluoridation propagandist has been caught misrepresenting the scientific literature on this issue. And his misleading press release is being touted as gospel truth by anti-fluoridation groups in NZ and the USA.

It is pathetic such people have to resort to misrepresentation in this way. Surely it is a sign of desperation to use statements that no conclusions were possible on specific details (adult benefits, social inequalities, influence of toothpaste, and what happens when fluoridation is stopped) because no studies fitted the selection criteria as “evidence” that there is no effect.


Griffin SO, Regnier E, Griffin PM, Huntley V. (2007). Effectiveness
of fluoride in preventing caries in adults. Journal of Dental
Research 2007;86(5):410–5.

Iheozor-Ejiofor, Z., Worthington, HV., Walsh, T., O’Malley, L., Clarkson, JE., Macey, R., Alam, R., Tugwell, P., Welch, V., Glenny, A. (2015). Water fluoridation for the prevention of dental caries (Review). The Cochrane Library, (6).

Maupomé, G., Clark, D. C., Levy, S. M., & Berkowitz, J. (2001). Patterns of dental caries following the cessation of water fluoridation. Community Dentistry and Oral Epidemiology, 29(1), 37–47.

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Misrepresenting the York fluoride review Ken Perrott Jun 16

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I have noticed a few “Letters to the Editor” and social media comments lately misrepresenting the “York review” on fluoridation so looked into the background of some of these claims.

The “York review” (McDonagh, et al., 2000) is one of the earliest authoritative and comprehensive reviews of the scientific literature related to fluoridation and resulted from a request by the UK Department of Health for:

“a systematic review of the evidence for the safety and effectiveness of water fluoridation based on the currently available evidence from population-based studies.”

As a systematic review it is a valuable resource for decision-makers so this review – together with later and more comprehensive reviews – is usually accepted as one of the most reliable sources of evidence for local bodies considering fluoridation  issues. However, this very authority leads to its misrepresentation by activists.

We are used to activists misrepresenting the evidence contained in such reviews, but I want to comment on the way anti-fluoride propagandists attempt to present the review authors as supporting anti-fluoride positions. In particular, the way they use quotes from anti-fluoride people who have some tenuous connection to the review. These quotes are presented as authoritative, consistent with the reviews findings and with the implications the people quoted were authors  or members of the York Fluoride Systematic Review Team – when they were not.

Review Team & Advisory Panel

The York Fluoride Systematic Review Team were the authors of the report. These authors and affiliation are:

  • Jos Kleijnen, NHS Centre for Reviews and Dissemination, York, UK
  • Marian McDonagh, NHS Centre for Reviews and Dissemination, York, UK
  • Kate Misso, NHS Centre for Reviews and Dissemination, York, UK
  • Penny Whiting, NHS Centre for Reviews and Dissemination, York, UK
  • Paul Wilson, NHS Centre for Reviews and Dissemination, York, UK
  • Ivor Chestnutt, Dental Public Health Unit, Cardiff, Wales, UK
  • Jan Cooper, Dental School, University of Wales College of Medicine, Cardiff, Wales, UK
  • Elizabeth Treasure, Dental School, University of Wales College of
    Medicine, Cardiff, Wales, UK

However, an advisory board was also appointed. This included representatives from “both sides of the fluoridation debate” as well as including neutral people. According to Richards et al., (2002):

“Although the advisory panel and review team agreed the results of the review, agreement was not reached about the conclusions or, more importantly, the implications of the review.”

Hardly surprising given the differing views on the issue. This article adds:

“Parties on each side of the controversy were reluctant to abandon their previous positions and endorse the review result whole-heartedly.”

The Systematic Review Advisory Panel members were:

  • Chair: Trevor Sheldon, York Health Policy Group, University of York, York, UK
  • Earl Baldwin of Bewdley, House of Lords, London, UK
  • Iain Chalmers, UK Cochrane Centre, Oxford, UK
  • Sheila Gibson, Glasgow Homeopathic Hospital, Glasgow, Scotland, UK
  • Sarah Gorin, Help for Health Trust, Winchester, UK
  • Mike Lennon, Chairman of the British Fluoridation Society, Department of Clinical Dental Sciences, University of
    Liverpool School of Dentistry, Liverpool, UK
  • Peter Mansfield, Director of Templegarth Trust, Louth, UK
  • John Murray, Dean of Dentistry, University of Newcastle, Newcastle
    upon Tyne, UK
  • Jerry Read, Department of Health, London, UK
  • Derek Richards, Centre for Evidence-Based Dentistry, Oxford, UK
  • George Davey Smith, Department of Social Medicine, University of Bristol, Bristol, UK
  • Pamela Taylor, Water UK, London, UK

Readers will see the mixed nature of this group so won’t be surprised there were fixed views which prevented their endorsement of the review findings and conclusions.

Opportunist quoting of minority views

Anti-fluoridation propagandists have made much of quotes from 2 advisory panel members – people who were not authors of the review and could not represent the review itself.


Out of context quote from anti-fluoride site No Fluoride.

Professor Trevor Sheldon has made a statement emphasising the provisional nature of the reviews findings, commenting on the poor quality of much of the research of health aspects and stressing the limitations of the review and need for further work. His statement recognised  that fluoridation is effective at reducing tooth decay The quality of research on health effects has also improved in recent years. However, anti-fluoride people use the quote in attempts to undermine research showing the efficacy of fluoridation and the lack of harmful effects. It is more correct to say, as Newton et al., (2015) did recently:

“In general, the literature suggesting adverse health effects of fluoridation is characterised by poor-quality studies that do not adequately adjust for potential confounding variables.”

Please note, Sheldon was a member of the Advisory panel and not an author of the review.

Another quote which has been rehashed recently by activists is from Advisory panel member Peter Mansfield:

“No physician in his right senses would prescribe for a person he has never met, whose medical history he does not know, a substance which is intended to create bodily change, with the advice, ‘Take as much as you like, but you will take it for the rest of your life because some children suffer from tooth decay.’”

Users of the quote imply he was an author of the review report – for example “Mansfield took part in the University of York (in York, England) review of public water fluoridation in 2000.” He did not. He was merely a member of the Advisory Panel representing the views of anti-fluoridationists. Have a search for him on the internet (he is the Director of Templegarth Trust, Louth, UK) to get a picture of his alternative health views.


In  their article about the York Review Richards et al., (2002) indicate that this early review identified problems with review processes and existing knowledge which future work would overcome:

“Future research can be more efficient and sharply focused as a result of open reviews of this kind. A consensus on future research priorities was one result of this review. The eventual findings of future work are more likely to be debated rationally and achieve wide consensus than if the review had not taken place.”

Anti-fluoride propagandists are simply taking advantage of those early issues, and dishonestly implying that they out-of-context quotes they use were made by authors of the York review when they weren’t.


McDonagh, M. S., Whiting, P. F., Wilson, P. M., Sutton, a J., Chestnutt, I., Cooper, J., … Kleijnen, J. (2000). Systematic review of water fluoridation. BMJ (Clinical Research Ed.), 321(7265), 855–9.

Newton, J. N., Young, N., Verne, J., & Morris, J. (2015). Water fluoridation and hypothyroidism: results of this study need much more cautious interpretation. Journal of Epidemiology and Community Health, 69(7), 617–8.

Richards, D., Mansfield, P., & Kleijnen, J. (2002). Systematic review in scientific controversy: the example of water fluoridation, an open access reviewEvidence-Based Dentistry, 3, 32–34.

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