Table 2. Comparison of risk difference, risk ratio, and odds ratio based on risks (p) and odds of two competitive groups (assume n = 1,000 per group).

	No. of event		Risk (p)		Odds		Risk difference	Risk ratio	Odds ratio
Example	Control	Tx.	Control (1)	Tx. (2)	Control (3)	Tx. (4)	(2) - (1)	(2) / (1)	(4) / (3)
1	1	2	0.001	0.002	0.001	0.002	0.001	2.000	2.000
2	5	10	0.005	0.010	0.005	0.010	0.005	2.000	2.000
3	10	20	0.010	0.020	0.010	0.020	0.010	2.000	2.000
4	15	30	0.015	0.030	0.015	0.031	0.015	2.000	2.067
5	50	100	0.050	0.100	0.053	0.111	0.050	2.000	2.096
6	100	200	0.100	0.200	0.111	0.250	0.100	2.000	2.252
7	200	400	0.200	0.400	0.250	0.667	0.200	2.000	2.668
8	200	700	0.200	0.700	0.250	2.333	0.500	3.500	9.333
9	500	200	0.500	0.200	1.000	0.250	−0.300	0.400	0.250
10	500	600	0.500	0.600	1.000	1.500	0.100	1.200	1.500
11	500	700	0.500	0.700	1.000	2.333	0.200	1.400	2.333
12	500	990	0.500	0.990	1.000	99.00	0.490	1.980	99.00
13	900	950	0.900	0.950	9.000	19.00	0.050	1.060	2.111
14	998	999	0.998	0.999	499.0	999.0	0.001	1.001	2.002