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Biostats Equation Table

Sensitivity Sensitivity = TP / (TP + FN)
Specificity Specificity = TN / (TN + FP)
PPV equation PPV = TP/(TP+FP)
NPV formula NPV = TN/(TN+FN)
Odds ratio OR = a/c / b/d
OR = ad/bc
used in case-control study
Relative Risk (RR) RR = [a/(a+b)]/©cohort studies
Positive likelihood ratio LR+ LR+ = Sensitivity/(1-Specificity)
Negative likelihood ratio LR- LR- = (1-sensitivity)/Specificity
Standardized Mortality Ratio (SMR) SMR = (observed # of deaths per year) / (expected # of deaths per year)
Attributable Risk (AR)AR = Risk exposed pts – Risk unexposed pts
AR = [A/(A+B)] – [C/(C+D)]
Attributable risk percentage (ARP) ARP = (Risk exposed- Risk unexposed)/risk exposed
Population attributable risk percent (PARP)PARP = (Risk in total pop- risk in unexposed)/ risk in total pop
Absolute Risk Reduction (ARR)ARR = [C/(C+D)] – [A/(A+B)]
Number needed to treat (NNT) equation NNT = 1/ARR
Number to needed to harm (NNH) equation NNH = 1/AR attributable risk