Academic debate is healthy and helps us to clarify the evidence base for the interested reader. However, it is unusual for a peer-reviewed paper in a reputable journal to receive quite as much criticism as that which greeted publication of the paper by Peckham et al on fluoride and hypothyroidism.1 Two highly critical commentaries were published at the time.2 ,3 A subsequent review article4 in the Journal of Evidence-based Dental Practice concluded that “this study is an ecologic one that has several significant flaws, making it almost meaningless with regard to assessing any possible association between water fluoridation and hypothyroidism.”

Published criticisms included lack of a coherent basis for a prior hypothesis, unbalanced citing of the literature, failure to allow for potential confounding, inadequate recognition of the limitations of ecological studies, imprecise measurement of exposure and outcomes, and over interpretation of the results to infer causation. Statistical aspects of the study were particularly heavily criticised by Warren et al4 for lack of transparency in reporting, the use of arbitrary categorical cut points to analyse a continuous variable, and by us3 for some apparently anomalous results in relation to deprivation.

The authors have now responded to the criticism and …