Applicability of multiple covariance analysis in caries studies

The relationship between pre- and posttreatment DMFS measures in clinical trials of dentifrices may be quadratic rather than linear and, if linear, the slope may differ from one. Given either of these eventualities the traditional DMFS increment measurement does not utilize all the information available in the pre-DMFS baseline score. If nonlinearity is present, analysis of multiple covariance with parameters derived from a polynomial regression is indicated.