# Formulae for MRCPsych

 .remove_background_ad { border: 1px solid #555555; padding: .75em; margin: .75em; background-color: #e7e7e7; } .rmbg_image { max-height: 80px; } Sensitivity A/(A+C)x100 Specificity D/(D+B)x100 Likelihood ratio for a positive test - definition LR shows how much more likely someone is to get a positive test if he/she has the disease, compared with a person without disease. Positive LR is usually a number greater than one and the negative LR ratio usually is smaller than one. Likelihood ratio for a negative test - definition Likelihood ratio for a positive test - formula Sensitivity/(1-Specificity) Likelihood ratio for a negative test  - formula (1-Sensitvity)/Specificity Negative predictive value - definition The proportion of patients with negative test who are actually free of the disease. This refers to the proportion of those scoring negative that don't have a condition (i.e. The chance that a negative result will be correct). Inversely proportional to prevalence. Negative predictive value - formula D/(D+C)x100 Positive predictive value - formula A/(A+B)x100 Positive predictive value - definition The proportion of patients with positive test who actually have the disease. Affected by prevalence - directly proportional. Pre-test probability (a+c)/(Total) Pre-test odds Pre-test probability/(1-pre-test probability) Post-test odds Pre-test odds x likelihood ratio for a positive result Accuracy (A+D)/Total Absolute risk reduction CER - EER Relative risk EER/CER Absolute risk reduction CER - EER Number needed to treat 1/ARR Standard error of the mean Standard deviation/√sample size Attributable risk proportion = AR/EER or (A/A+B) - (C/(C+D)) % results within 2 SD of mean? 95.4% Relative risk reduction (CER - EER)/CER Standard deviation √variance .remove_background_ad { border: 1px solid #555555; padding: .75em; margin: .75em; background-color: #e7e7e7; } .rmbg_image { max-height: 80px; } AuthorEm262 ID339307 Card SetFormulae for MRCPsych DescriptionFormulae to know for MRCPsych Paper B Updated2018-04-09T07:36:39Z Show Answers