# ============================================================
# Odds Ratio, Relative Risk & NNT
# Biostatistics in R — Rverse Analytics
# https://rverseanalytics.com/learn-biostatistics/orrr
# ============================================================

# Odds ratio, relative risk & NNT from a 2x2 table
# exposed group: events / non-events
exp_event <- 30; exp_none <- 70
# control group: events / non-events
ctrl_event <- 15; ctrl_none <- 85
# Odds ratio and relative risk
OR <- (exp_event * ctrl_none) / (exp_none * ctrl_event)
RR <- (exp_event / (exp_event + exp_none)) / (ctrl_event / (ctrl_event + ctrl_none))
c(odds_ratio = OR, relative_risk = RR)
# Absolute risk reduction & number needed to treat
risk_exp  <- exp_event  / (exp_event  + exp_none)
risk_ctrl <- ctrl_event / (ctrl_event + ctrl_none)
ARR <- risk_ctrl - risk_exp
c(ARR = ARR, NNT = 1 / abs(ARR))