From normal distribution to diagnostic test

Distribution curves of laboratory parameters in healthy and sick subjects are quite similar, leading to a “grey zone” referred to subjects that could be not correctly identified and classified. To identify a cut-off value, ROC (Receiver Operating Characteristics) curves can be applied; they represent the graphic relationship between sensibility (true positive) and specificity (false positive), depending on cut-off values variability. ROC curve subtends AUC (Area Under the Curve); AUC's width is directly related to discerning power of any validated statistical test. (Epidemiology_statistics)