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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 |
