By Ken Perrott 16/08/2015


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According to a recently published survey, only 15% of New Zealanders are opposed to community water fluoridation (CWF).

Only 15% – yet anti-fluoride propagandists are using the same survey (or their limited reading of it) to claim that 58% of New Zealanders are opposed to (or do not support) CWF! (See Fluoridation problem for New Zealand, Most NZers do not support fluoridation, study saysFLUORIDATION’S FALLING POPULARITY NO SURPRISE, and Fluoridation’s Falling Popularity No Surprise.) That’s a huge difference. Someone must be using statistics in a creative way – or just outright lying.

The survey results were published in this paper:

Whyman, R. A., Mahoney, E. K., & Børsting, T. (2015). Community water fluoridation: attitudes and opinions from the New Zealand Oral Health Survey. Australian and New Zealand Journal of Public Health.

So anyone can check it out – although I recommend, as always, to read the full text. Often abstracts do not give the full information you want.

This survey reports data for various questions, but Table 2: “Estimates of ‘how in favour of water fluoridation’ (unweighted n, weighted percentage with 95% CI) opinions among adults (>=18 years of age)” is the relevant one here. The graphics below summarise the overall message (vertical bar is the 95% CI):

Whyman-1

Or simplifying further into “for,” “against,” “neutral” and “do not know:”

Whyman-2

So you can see the cherry-picking Mary Byrne from Fluoride Free NZ indulged in for her press release Most NZers do not support fluoridation, study says where she claims:

“This is the finding of a new survey carried out by Hawke’s Bay District Health Board: 58% of people did not support fluoridation even “somewhat”. This shows that people are really clear – New Zealanders do not agree with adding an industrial by-product, classified as hazardous, to our drinking water.”

She, no doubt would be offended by a claim that 85% of people support (or do not oppose) fluoridation – strongly or somewhat. Yet, her cherry picking is just as bad.

The real message from this survey for the anti-fluoride campaigners is that only 15% are opposed to community water fluoridation (CWF) – and then only 10% are strongly opposed.

As for the “creative license” of Mary Byrne and her fellow anti-fluoride propagandists, this message I picked up from a statistician’s cartoon sums it up:

You’ve heard of ‘Lies, Damn Lies, and Statistics.’ Well, apparently, they WERE lying about the statistics.”

The real message from the survey

The authors of this report did concentrate on the figure for those supporting CWF, or more importantly, the large proportion of people who are neutral (20%) or feel they just do not know enough to decide (22%). Interestingly, if these are excluded (as probably happens in referenda where a yes or no answer is required so that the neutral and undecided may not vote) the survey’s data translate into about 74% of the population supporting CWF and 26% opposing it. Not too different to recent referenda results (ranging from 58.1% support in Whakatane to 76.4% support in South Waikato).

However, health authorities are right to be concerned about the relatively large number of neutral and undecided people. The 15% who are opposed to CWF may largely be a “lost cause” because of their ideological stubbornness. But the data does show a need for more information on CWF and oral health in general.  It is likely that a better-informed population on this issue would lead to lower numbers of neutral and “do not know” people – and, very likely, a larger number of those who support CWF.

I have simply mentioned here the overall figures for support of, and opposition to, CWF but the study goes into a lot more detail and identifies sectors of the population requiring better education on the subject. Hopefully, we will see suitable oral health education programmes in future and a reduction in the neutral and “don’t know” numbers.

That can only be a good thing.

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