Also called the true positive rate. Measures the proportion of positives that are correctly identified as such (e.g., the percentage of  people with the disorder of interest who are correctly identified as having the condition). Calculated as TP/TP+FN where TP is true positives (have the disease and test positive) and FN is false negatives (have the disease, test negative).  Helpful when you know how many laboratory samples are truly positive for disease and you want to know how many of these will be detected. However, in an office setting, you are typically screening otherwise normal individuals and do not know who does and who does not have a condition.  Therefore, positive predictive value (PPV) becomes very important as this answers the meaningful clinical question of what is the chance that an otherwise healthy individual actually has the condition if the screening test is positive.