Common statistical tests

A recent survey by BeGole of four major orthodontic journals revealed that 76% of the original and scientific articles published in 1997 incorporated statistical procedures in their methodologies. To evaluate the information presented in these scientific articles, the clinician needs to have an understanding of the statistical techniques used in them. Although a number of the statistical methodologies were complex, requiring considerable statistical sophistication to understand and apply, the majority of the statistical methods that were used were more easily understood. The purpose of this article is to familiarize the orthodontic clinician with those statistical procedures commonly encountered in the orthodontic literature. Actual formulas and computations are not reviewed in this article and can be found in standard statistical texts. The focus of this article is to emphasize the appropriate use of techniques such as the Student t test, analysis of variance, the X² test, and the nonparametric alternatives to these methods, which comprise more than 50% of the statistical tests used in the journals from 1997 examined by BeGole.