It was a joy to see diagnostic test methodology applied in the article by Amendt et al entitled, “Validity and Reliability Testing of the Scoliometer®” (Phys Ther. 1990;70:108–117). Furthermore, as diagnostic test methodology is relatively new to the physical therapy literature, I was encouraged to see that the authors elected to elaborate on four of the key terms (ie, sensitivity, specificity, positive predictive value, and negative predictive value) relevant to this topic. Given this methodology is relatively new to our literature, I feel it is important to highlight an additional point: the impact that prevalence has on the predictive values of a test. This relationship has relevance to the interpretation of the predictive values reported by Amendt et al, and, in order to provide an example of this relationship, I will refer to results presented in their article. David H Nielsen, PhD, PT Associate Professor, Physical Therapy Education, 2600 Steindler Bldg, The University of Iowa, Iowa City, IA 52242 Carolyn T Wadsworth, PT Lecturer, Physical Therapy Program, The University of Iowa