Logical and analytic issues in dental/oral product comparison research

Possible meanings of "superiority" and "equivalence" in comparative dental studies are considered. A proposed refinement of vocabulary is introduced to precisely distinguish between these meanings. Implications for data analysis of different interpretations of "superiority" and "equivalence" are explored, as are implications for study design where design and analytic considerations are inseparable. Conceptual problems of equivalence studies are stressed. Choice of analytic unit(s), scaling of dependent variables, use of surrogate variables, and validity checking are discussed as they pertain to comparative studies. Analytic methods for correlated responses and categorized responses are briefly surveyed, particularly with reference to periodontal research.