Statistical Aspects of Design and Analysis of Clinical Trials for the Prevention of Caries

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Abstract
This paper considers the methods used in design and analysis of recent clinical trials of topical fluoride interventions designed to prevent the development of dental caries in children, with particular consideration given to issues related to cluster-randomized trials. Studies which met the inclusion criteria were recent clinical trials of topical fluoride interventions published since 1990, conducted in children under 16 years of age, with caries as the outcome variable. Papers not published in English were translated. Information was extracted from the published trial reports on the units of randomization and analysis. The papers were also studied to assess if reporting allowed the assessment of potential consent bias in cluster-randomized trials and the reproduction of sample size calculations. Fifteen trials published since 1990 were included, of which five were cluster randomized. Only 1 of the 5 accounted for the clustering in the analysis. For the other four trials, it was possible to calculate that values from 0.002 (for DMFS) and 0.08 (for being caries free) for the intracluster correlation coefficient within schools could result in statistically non-significant findings. 3 of the 5 cluster-randomized trials did not report the consenting procedure in enough detail to judge whether consent bias could be present. Only 1 of the total 15 trials reported a sample size calculation. In summary, researchers should be aware of the importance of correctly analyzing cluster-randomized data and thorough reporting of clinical trials according to the CONSORT guidelines.