Table 1

A 2×2 table showing the cross-classification of index test and reference standard results and overview of measures of accuracy that can be calculated from these data*

 True positives People with the target condition who have a positive test result TP True negatives People without the target condition who have a negative test result TN False positives People without the target condition who have a positive test result FP False negatives People with the target condition who have a negative test result FN Sensitivity Proportion of patients with the target condition who have a positive test result TP/(TP+FN) Specificity Proportion of patients without the target condition who have a negative test result TN/(FP+TN) Positive predictive value (PPV) Probability that a patient with a positive test result has the target condition TP/(TP+FP) Negative predictive value (NPV) Probability that a patient with a negative test result does not have the target condition TN/(FN+TN) Prevalence The proportion of patients in the whole study population who have the target condition (TP+FN)/(TP+FP+FN+TN) Positive likelihood ratio (LR+) The number of times more likely a person with the target condition is to have a positive test result compared with a person without the target condition (TP/(TP+FN))/(FP/(FP+TN)) or sensitivity/(1−specificity) Negative likelihood ratio (LR−) The number of times more likely a person with the target condition is to have a negative test result compared with a person without the target condition (FN/(TP+FN))/(TN/(FP+TN)) or (1−sensitivity)/specificity
• *Adapted from Whiting P, Martin RM, Ben-Shlomo Y, et al. How to apply the results of a research paper on diagnosis to your patient. JRSM Short Reports 2013;4:7.

• FN, False negatives; TP, true positives.