Group | Outcome (N° of study participants) | Risk/odds | ||

Stroke | No stroke | Total | ||

Intervention (dietary supplement) | 20 | 80 | 100 | Risk (R(i)): 20/100=0.2 Odds (O(i)): 20/80=0.25 |

Control (placebo) | 25 | 75 | 100 | Risk (R(c)): 25/100=0.25 Odds (O(c)): 25/75=0.33 |

Absolute risk reduction or risk difference: R(c) – R(i) = 0.25 – 0.2 = 0.05 (5%).

Relative risk: R(i)/R(c)=0.2/0.25=0.8 (80%).

OR: O(i)/O(c)=0.25/0.33=0.76 (76%).

Relative risk reduction: 1 − RR = 0.2 (20%).

Relative odds reduction: 1 − OR = 0.24 (24%).

Number needed to treat=1/ARR=20.

ARR, absolute risk reduction; NNT, number needed to treat; O(c), odds of stroke with control; O(i), odds of stroke with intervention; R(c), risk in control group; RD, risk difference; R(i), risk in intervention group; ROR, relative odds reduction; RR, relative risk; RRR, relative risk reduction.