Temporomandibular disorder literature contains serious misunderstandings and misapplications of statistical concepts, including predictive values, in evaluating diagnostic modalities and in clinical decision making. The use of general population prevalence data for temporomandibular disorders to evaluate positive predictive values of diagnostic modalities is shown to be invalid. The positive predictive value of a diagnostic tool should not be used to evaluate the efficacy of the tool or to confirm the presence of temporomandibular disorders when the pretest likelihood of temporomandibular disorder is low (eg, 10%). In such a situation, the TMJ Scale's negative predictive value of 98% supports the dentist's clinical impression of the absence of temporomandibular disorders. When the pretest likelihood of TMD is high (eg, 90%), the TMJ Scale's positive predictive value of 97% supports the dentist's clinical impression of the presence of temporomandibular disorders. The predictive values of the subscales of the TMJ Scale that measure joint dysfunction and stress may be used to further refine the diagnostic impression. When the dentist is unsure of the presence of TMD and makes a pretest estimate of 50%, the TMJ Scale's positive predictive value of 81% and negative predictive value of 83% substantially improve the accuracy of clinical decisions.