Letters

Water fluoridation and tooth decay in 5 year olds

BMJ 1998; 316 doi: https://doi.org/10.1136/bmj.316.7126.230a (Published 17 January 1998) Cite this as: BMJ 1998;316:230

Samples were unequal and too small

  1. Tiemo Vemmer, Doctora
  1. aMünsterstrasse 33, D-22529 Hamburg, Germany
  2. bGlasgow Homoeopathic Hospital, Glasgow G12 0NR
  3. c354 Albert Drive, Glasgow G41 5PJ
  4. *Sheila and Robin Gibson are medical and dental advisers to the National Pure Water Association.
  5. dWigan and Bolton Health Authority, Wigan WN1 1AH
  6. eWest Pennine Health Authority, Oldham OL1 2PL
  7. fNewcastle Health Authority, Newcastle upon Tyne NE6 4PF
  8. gEast Lancashire Health Authority, Nelson, Lancashire BB2 5SZ
  9. hShropshire Health Authority, Shrewsbury SY3 8XL

    Editor-Jones et al reported an association between water fluoridation, social deprivation, and tooth decay in 5 year olds; they found that the more deprived the area the more it benefited from water fluoridation.1 This conclusion may be considered premature, as the study had several flaws.

    Firstly, Jones et al do not state whether the populations of the different wards were comparable or whether less privileged areas had a higher proportion than did more affluent wards of non-white subjects born in countries other than the United Kingdom. One of the items of the Jarman score is the proportion from ethnic minorities (“new Commonwealth and Pakistan”).2 The observed differences between less and more deprived wards possibly did not reflect differences in social deprivation but were caused by ethnic or cultural differences, or both-for example, differences in nutrition (consumption of sticky oriental sweets) and attitudes to and accessibility of dental care, etc. The authors did not adjust for such differences.

    Secondly, why did the authors use data from the 1991-2 NHS dental surveys for the fluoridation areas and from 1993-4 for the non-fluoridation area?

    Thirdly, the number of subjects per ward was unequal (range 13-264). As the ward of 13 subjects and the one of 264 were weighted equally the results are biased towards wards with few subjects. Also, minor statistical fluctuations are more likely to influence the results in wards with few subjects. Therefore the calculation of a 44% reduction in tooth …

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