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.