Abstract
The aim of this study was to develop an index for selection of those subjects able to increase the discriminatory ability of experimental clinical trials of caries prophylactic agents. The index, DMFS(e), excludes from the calculation of initial DMFS all occlusal surfaces of permanent first molars and any of those teeth extracted due to caries. Data from four clinical trials, three with placebo and one with an active control, were examined retrospectively. Subjects were initially aged 11-12 yr. The efficiency of the DMFS(e) index was compared to DMFS for selection of discriminating subgroups by the calculation of minimum sample sizes required to attain statistical significance (alpha = 0.05, beta = 0.2). For each trial, the DMFS(e) index was more efficient. Specific criteria were established for those subjects who consistently failed to contribute to the study results. Following exclusion of those subjects, considerable saving in minimum sample size was achieved, the greatest reduction occurring in the active control trial.
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