By Ken Perrott 05/04/2016


Anti-fluoride campaigners seem to be a sixes and sevens on whether community water fluoridation (CWF) is effective or not. Some will accept CWF is effective in improving oral health but moan about the ethics or reports of harm. Others will simply claim CWF is not effective.Stans-lie-annot

Stan Litras is a Wellington dentist and anti-fluoride campaigner in the latter camp. He continually denies that CWF is effective and claims he has science to back up his claim. However, what he actually means is that if he cherry-picks the science, holds his mouth the right way and prevents you from looking at the context and data – he can find a quote to support his position.

I have debunked his claims before in my articles – such as, Cherry-picking and misinformation in Stan Litras’s anti-fluoride article and Cherry-picking and misinformation in Stan Litras’s anti-fluoride article. But he is at it again. This time he is misrepresenting a recent New Zealand research paper in a recent letter to the Christchurch Press.

There are several misrepresentations in his letter but here I will just take issue with the highlighted text. Stan claims:

“The DHB’s Dr Martin Lee published a research paper recently which showed little or no benefit from water fluoridation, a finding consistent with the modern weight of evidence.”

It is always best to check out such claims and I have hunted down the paper Stan probably refers to. It is:

Schluter, P. J., & Lee, M. (2016). Water fluoridation and ethnic inequities in dental caries profiles of New Zealand children aged 5 and 12–13 years: analysis of national cross-sectional registry databases for the decade 2004–2013. BMC Oral Health, 16(1), 21.

This is linked to the full-text version so readers can check out the paper itself.

Far from showing “little or no benefit” from water fluoridation the abstract actually says:

“Significant and sustained differences were observed between Māori and non-Māori children, and between CWF and non-CWF exposed groups.”

Stan ignored that sentence but latches on to (or cherry-picks) the next sentence:

“However, a convergence of dental profiles between non-Māori children in CWF and non-CWF regions was observed.”

But he ignores completely the authors’ discussion of this apparent convergence. Obviously, the discussion doesn’t support Stan’s anti-fluoride bias! But that discussion is interesting and worth considering.

Is there a convergence?

I have noted this convergence before in my articles Cherry picking fluoridation data and Fluoride debate: Response to Paul’s 5th article where I used similar data to that used in Schluter & Lee (2016). That data is available on the Ministry of Health’s website.

The graphs below show the raw data for all (“total”) children and for Māori:

% CARIES FREE

MEAN DECAYED, MISSING AND FILLED TEETH

So, yes, there is a convergence in the sense that the differences in the oral health of children in fluoridated and unfluoridated areas appears to be reducing with time. I have speculated that the apparent convergence could have something to do with the introduction of “hub and spoke” dental clinics after 2004. One problem with this raw data is that children are allocated according to the fluoridation status of thew school – rather than their residence. This will lead to incorrect allocation in some cases.

However, this paper suggests another reason for the convergence which I hadn’t considered.

Changes in and composition of the non-Māori group

The authors say:

“Another notable feature was the apparent convergence of prevalence estimates amongst non-Māori children in CWF and non-CWF areas. It is likely that a substantial driver of this convergence was due to significant changes within the dynamic and heterogeneous non-Māori groups both within and between DHB regions. In effect, the ecological fallacy – a logical flaw whereby analyses of group data are used to draw conclusions about an individual – may be operating within the non-Māori group.”

This is interesting and is supported by the data.

First, let’s note that while I compared data for Māori children with the total data in my figures above these authors have actually compared data for Māori and non-Māori. This shows a clearer convergence for non-Māori children than for all children – see this figure for 5-year-old children from the paper (dmft = decayed, missing and filled teeth per child):

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Fig. 1 No obvious decay experience (caries-free) percentages and mean dmft for 5-year old children over years 2004 to 2013, partitioned by Māori and non-Māori ethnicities and fluoridated (F) and non-fluoridated (NF) areas

The picture is similar for year 8 children.

So you can see why anti-fluoride campaigners would love to cherry pick the non-Māori data. I predict that Stan and other anti-fluoridation campaigners will be reproducing parts of this figure in their propaganda for future use.  That graph is just too good for them not to cherry-pick.

But we need to remember that the non-Māori group is not ethnically uniform. In particular, Pacifica make a large contribution to this group. That contribution is unevenly distributed between the fluoridated and fluoridated groups. And it has changed over time.

  • In 2013 about 86% of Pacific live in fluoridated areas – over the period covered by these MoH records this proportion has varied between 80 and 90%.
  • In 2013 Pacifica make up about 12% of the non-Māori group (between 2007 and 2o13 this has varied between 9.0 and 12.7%)
  • In 2013 Pacific make up about 19.3% of the non-Māori fluoridated group (between 2007 and 2013 this has varied between 14.9 and 20.7% of the non-Māori fluoridated group).

MoH data confirms problem of Pacific inclusion

So the oral health of Pacifica can have a relatively large influence on the data for the non-Māori group – particularly for the fluoridated non-Māori group where they are included. This becomes important when we realise that the oral health of Pacifica is markedly poorer than for the rest of the non-Māori group. I have illustrated this using the average of data for fluoridated 5-year-olds in the period 2007 – 2013.

other-pacifica-310b4d968a1cc594015fc665ecf49256a8e15018

Data for 5-year-old children. dmft = decayed, missing and filled teeth. The “other” group is non-Māori and non-Pacifica

So the poorer oral health of Pacifica will drag down the % caries free and drag up the mean dmft data for the fluoridated non-Māori group. However, this will have little influence on the unfluoridated non-Māori group because of the very small Pacific contribution.

We can confirm this with the raw data from the Ministry of Health website. That data is given separately for Māori, Pacifica and “other” (non-Māori/non-Pacific). The figure below shows this data for the 5-year-old children.

other-a349beb9a40a535be7433d1b802bb99ed6730ab0

Comparison of data for “other” (non-Māori/non-Pacifica) children in fluoridated (F) and unfluoridated (UF) areas.

OK – there is still some evidence of convergence from about 2007 on between fluoridated and unfluoridated children. But the graphs do indicate that CWF is still having  a beneficial effect.

But I think Stan and his mates will prefer to cherry-pick the data for the non-Māori group and keep very quiet about the distorting effect that inclusion of Pacific in this group has had on the apparent convergence.

Note: I have used the raw Ministry of health data in this discussion. Schluter & Lee (2016) used standardised estimates to account for the difference in the numbers of unexamined children according to ethnicity.