Diagnostic test calculations from a 2×2 table (disease present/absent × test positive/negative):

Treatment effect calculations from a 2×2 table (treated vs control × event vs no event):

Risk_treated = events_treated / total_treated
Risk_control = events_control / total_control
Relative risk (RR) = risk_treated / risk_control
Odds ratio (OR) = (events_treated × non-events_control) ÷ (non-events_treated × events_control)
Absolute risk reduction (ARR, %) = 100 × (risk_control − risk_treated)
Relative risk reduction (RRR, %) = 100 × (risk_control − risk_treated) / risk_control
Number needed to treat (NNT) = 1 ÷ (risk_control − risk_treated)

Basic Statistics Calculator