Box 9.2.a: Calculation of RR, OR and RD

This is an archived version of the Handbook. For the current version, please go to training.cochrane.org/handbook/current.

Box 9.2.a: Calculation of risk ratio (RR), odds ratio (OR) and risk difference (RD) from a 2×2 table

The results of a clinical trial can be displayed as a 2×2 table:

Event

(‘Success’)

No event

(‘Fail’)

Total

Experimental intervention

S_E

F_E

N_E

Control intervention

S_C

F_C

N_C

where S_E, S_C, F_E and F_C are the numbers of participants with each outcome (‘S’ or ‘F’) in each group (‘E’ or ‘C’). The following summary statistics can be calculated: