The Real Role of Sensitivity, Specificity and Predictive Values in the Clinical Assessment

Journal of Clinical Sleep Medicine, Vol. 12, No. 2, 2016 We would like to thank Dr. Raphael, because her letter 1 published in this issue of the Journal of Clinical Sleep Medicine provides us with an opportunity to emphasize points already highlighted in our article. The main goal of our study was to evaluate the diagnostic ability of signs and symptoms of sleep bruxism (SB) according to the criteria of the American Academy of Sleep Medicine (AASM) and a diagnostic classification system proposed by international experts to assess SB. The validity of a diagnostic test is determined as the ability of a test to tell who have the disease from who do not. For this purpose, two components are calculated: sensitivity and specificity. Sensitivity is the ability to correctly identify those who have the disease, while specificity is the ability to correctly identify those who do not have the disease.2 In order to calculate sensitivity and specificity, it is required that patients be identified by another test which provides a more permanent result, is often more sophisticated, more invasive, and more expensive, named gold standard.2 In our study, the polysomnography (PSG) was considered the gold standard for SB assessment. The evaluation of the validity of a diagnostic test is usually performed on selected contexts as well, with two equally-numbered groups of patients—one with the disease, one without it—as this is an efficient way of describing sensitivity and specificity.3 Having that in mind, we selected a control group with the same number of patients as the group of patients with the disease for the sample, then we calculated the sensitivity and the specificity of each tested diagnostic criteria. We know that sensitivity and specificity are characteristics of the diagnostic test, although the predictive value is also influenced by the prevalence.3 That is why when we want to evaluate the discriminatory capacity of a particular diagnostic test, we calculate sensitivity and specificity, even though the predictive values are clinically more useful.2 In our study, besides the main measures to determine accuracy, we chose to present additional analyses reporting predictive values of each test, which were calculated based on the prevalence of our sample LETTERS TO THE EDITOR