Anti-fluoridationists misrepresent New Zealand dental data – an annual event

Caught again! – NZ anti-fluoride campaigners tell their annual porky about the MoH statistics for the dental health of school children.

This exercise in confirmation bias by New Zealand anti-fluoridation campaigners has become an annual tradition involving confirmation bias and cherry-picking. Every year the Ministry of Health (MoH) releases a spreadsheet containing the most recent data on school children’s dental health. And every year the Fluoride Free NZ (FFNZ) activists select some figures from the spreadsheet to argue their case that fluoridation is not effective. A simple exercise in bias confirmation by cherry picking.

I wrote about last year’s exercise in my article Anti-fluoridationists misrepresent new dental data for New Zealand children. That involved the MoH data for 2015. My comments on their misrepresentation of the newly released 2016 data will be much the same.

FFNZ claims the 2016 statistics:

“show absolutely NO difference in dental decay rates between five year olds in fluoridated areas compared to non-fluoridated areas.”

Notice the specifics – 5-year-olds. And no mention of ethnicity. They have simply used the total figures (which mislead because of effects of ethnic differences) and cherry-picked the specific data where the figure for fluoridated areas and non-fluoridated areas are very close.

What does the new data really say?

Let’s look at a summary of the data – for 5-year-olds and year 8 children – and for the different ethnic groups listed – Māori, Pacific Island and “other”(mainly Pakeha and Asian).  You can download the spreadsheets contain the data from the MoH web page – Age 5 and Year 8 oral health data from the Community Oral Health Service. We will look at the % of these children that a free from caries as well as the mean decayed, missing and filled teeth (dmft and DMFT) for each group.

5-year-olds

Notice the FFNZ cherry picking? Yes, the “Total” figures show very little difference but if they had dared look at different ethnic groups their argument would not have looked so great. Fluoridation appears to be associated with an improvement of dental health from about 6% (for “Other”) to 23% (for Māori)

Year 8 children

You can see why  FFNZ chose the 5-year-olds instead of year 8 children. Even the misleading data for the “Total” group suggests an almost 20% improvement of dental health in fluoridated areas.  Fluoridation appears to be associated with an improvement of dental health from about 18% (for “Other”) to 30% (for Māori)

Importance of ethnic classifications.

The figures above show big differences between ethnic groups, with the dental health of Pacific Island children being the worst.

This is an important factor because most Pacific Island children live in fluoridated areas – about 85%. The figure below shows the distribution of the two different age groups.

This means that the overall, or “Total” data is distorted. Pacific Island children predominance in fluoridated areas increase the value of dmft/DMFT and lowers the value of caries-free % in the fluoridated areas.

So the FFNZ activists are not only cherry picking to confirm a bias – they have selected the figures which are most distorted by ethnic differences.

Far from the latest data showing “absolutely NO difference” it actually shows differences of the order of 18 -30%.

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