Research and Statistics: Sensitivity, Specificity, Predictive Values, and Likelihood Ratios

Abstract

1. Diana N. Carvajal, MD* 2. Peter C. Rowe, MD* 1. *Department of Pediatrics, Division of General and Adolescent Medicine, Johns Hopkins University School of Medicine, Baltimore, Md. You are seeing a previously healthy 5-year-old girl in your office for a complaint of sore throat and fever. Her mother explains that the child does not have a cough, but she has had a decreased appetite and unusual fatigue over the past 1 to 2 days. Physical examination reveals a slightly ill-appearing child who has an erythematous oropharynx, mild cervical adenopathy, and a temperature of 37.5°C. A white blood cell (WBC) count from the previous evening was 9.2×103/mcL (9.2×109/L). According to the mother, her daughter had similar symptoms last year, but she is sure it was not a streptococcal throat infection, and the symptoms resolved without treatment. She asks you whether the current presentation is a streptococcal throat infection that requires antibiotic treatment. Based on the history and physical examination findings, you decide on the basis of your experience that there is about a 30% chance of bacterial pharyngitis. You recall an article discussing the effectiveness of the Breese clinical scoring system for the diagnosis of group A beta-hemolytic Streptococcus (GABHS) pharyngitis. (1) You consider whether the results of this study are valid and relevant to your current patient. (2) For clinicians, it is important to understand and interpret the effectiveness of certain diagnostic tests, especially when such great advancements are being made in medical technology. The usefulness of a test can be determined by how accurately it identifies the target disorder. (3) It is important to know about the properties of individual tests and how each test compares with the gold standard (reference test). (2)(3) The pretest probability of a …