Table 6.

Type I error and power for the 95% CI of the proportion mediated effect: ab/(ab + c′)

	Sample size
Population parameters	50	100	200	500	1,000
Type I error
c′ = 0
Zero effect: a = b = 0	0	0	0	0	0
c′ = 0.14
Zero effect: a = b = 0	0	0	0	0	0
c′ = 0.39
Zero effect: a = b = 0	0	0	0	0	0
c′ = 0.59
Zero effect: a = b = 0	0	0	0	0	0
Power
c′ = 0
Small effect: a = b = 0.14	0	0	0	0.01	0.04
Medium effect: a = b = 0.39	0.05	0.20	0.49	0.91	0.99
Large effect: a = b = 0.59	0.49	0.87	0.99	1	1
c′ = 0.14
Small effect: a = b = 0.14	0	0	0.01	0.36	0.94
Medium effect: a = b = 0.39	0.14	0.58	0.96	1	1
Large effect: a = b = 0.59	0.74	0.98	1	1	1
c′ = 0.39
Small effect: a = b = 0.14	0.01	0.02	0.10	0.57	0.97
Medium effect: a = b = 0.39	0.32	0.86	1	1	1
Large effect: a = b = 0.59	0.92	1	1	1	1
c′ = 0.59
Small effect: a = b = 0.14	0	0.02	0.11	0.58	0.97
Medium effect: a = b = 0.39	0.38	0.88	1	1	1
Large effect: a = b = 0.59	0.93	1	1	1	1