Table 1.

Fitted mean of sample size and 95% confidence interval back transformed from logarithmic values, type III F statistic and the corresponding p value of the effect of class of prevalence on sample size adjusting for phase and interaction between prevalence and phase, and without adjustment for other covariates and with adjustment for other covariates^a

Characteristics		Without adjustment for other covariates					With adjustment for other covariates
		No. of trials, m	Fitted mean	95% CI	F test	p value	No. of trials, m	Fitted mean	95% CI	F test	p value
Prevalence class					17.38	<.0001				20.73	<.0001
<1/1,000,000		19	21.21	(11.63–38.67)			18	28.61	(14.43–56.73)
1–9/1,000,000		88	40.57	(32.18–51.14)			66	55.23	(33.76–90.37)
1–9/100,000		587	74.19	(67.71–81.29)			483	90.09	(58.66–138.36)
1–5/10,000		454	86.37	(78.32–95.25)			359	93.10	(60.58–143.08)
Phase of investigation b					21.56	<.0001				324.97	<.0001
Phase 2		841	32.84	(28.61–37.69)			677	46.34	(29.86–71.90)
Phase 3		307	71.50	(53.05–96.38)			249	78.57	(47.48–130.02)
Prevalence × Phase					6.40	0.0003				2.75	0.0415
Phase 2	<1/1,000,000	16	18.05	(11.20–29.09)			15	26.96	(14.74–49.31)
	1–9/1,000,000	65	35.23	(27.80–44.65)			48	49.04	(29.87–80.51)
	1–9/100,000	442	41.52	(37.92–45.47)			365	58.70	(38.14–90.32)
	1–5/10,000	318	44.04	(39.57–49.02)			249	59.42	(38.62–91.43)
Phase 3	<1/1,000,000	3	24.92	(8.28–75.06)			3	30.37	(10.37–88.92)
	1–9/1,000,000	23	46.71	(31.37–69.56)			18	62.21	(34.40–112.49)
	1–9/100,000	145	132.56	(113.12–155.35)			118	138.28	(88.39–216.34)
	1–5/10,000	136	169.39	(143.80–199.53)			110	145.86	(92.79–229.30)

^aGender, age, whether or not the trial had a DMC, whether or not the intervention was FDA regulated, intervention model, trial regions, number of countries participating in the trial, year that enrolment to the protocol begins and number of arms

^bAs defined by the US FDA for trials involving investigational new drugs