Ridit analysis in dental clinical studies

Ridit analysis is presented as an appropriate method of analyzing dental clinical data which fall somewhere between the purely categorical (e.g., improved vs. not improved) and the bona fide quantitative (e.g., mg % salivary calcium) scales of measurement. The key feature of the method is the estimation of the probability that a randomly-selected patient from one treatment group is "better-off" than a randomly-selected patient from another. Methods are presented for testing statistical significance and constructing confidence intervals. The method is illustrated on data from a comparative clinical trial of ibuprofen, aspirin and placebo in the relief of post-extraction pain. There were no significant differences in efficacy among the active treatments, but each was significantly superior to placebo.