Table 3.

Recruitment properties of the studies audited, stratified by presence of an internal pilot

		Internal pilot (N = 97)	No internal pilot (N = 37)	Total (N = 134)
Total target sample size	n	97	36	133
	Mean (SD)	945.1 (1400.0)	1171.8 (1460.3)	1006.5 (1414.6)
	Median (IQR)	510.0 (350.0, 900.0)	625.0 (395.0, 1,349.2)	533.0 (360.0, 1,044.0)
	Minimum, maximum	120, 9920	100, 8000	100, 9920
Recruitment target for internal pilot	n	69	–	69
	Mean (SD)	135.2 (156.8)	–	135.2 (156.8)
	Median (IQR)	100.0 (48.0, 162.0)	–	100.0 (48.0, 162.0)
	Minimum, maximum	20, 1165	–	20, 1165
Proportion of sample size aimed to be recruited in internal pilot (%)	n	69	–	69
	Mean (SD)	18.5 (10.4)	–	18.5 (10.4)
	Median (IQR)	15.8 (10.2, 25.0)	–	15.8 (10.2, 25.0)
	Minimum, maximum	2.3, 50	–	2.3, 50
Length of recruitment for full study (months)	n	96	35	131
	Mean (SD)	28.6 (10.9)	22.3 (9.1)	26.9 (10.8)
	Median (IQR)	24.0 (20.8, 36.0)	20.0 (16.5, 30.0)	24.0 (18.0, 36.0)
	Minimum, maximum	11, 60	5, 45	5, 60
Length of recruitment for internal pilot (months)	n	96	–	96
	Mean (SD)	9.4 (5.1)	–	9.4 (5.1)
	Median (IQR)	8.5 (6.0, 12.0)	–	8.5 (6.0, 12.0)
	Minimum, maximum	3, 30	–	3, 30
Proportion of recruitment length used in internal pilot (%)	n	95	–	95
	Mean (SD)	33.5 (12.6)	–	33.5 (12.6)
	Median (IQR)	33.3 (25.0, 40.8)	–	33.3 (25.0, 40.8)
	Minimum, maximum	9.4, 68.8	–	9.4, 68.8
Number of centres involved in full study	n	91	30	121
	Mean (SD)	20.9 (22.1)	19.9 (17.1)	20.6 (20.9)
	Median (IQR)	14.0 (7.5, 25.0)	15.5 (6.0, 29.0)	14.0 (7.0, 26.0)
	Minimum, maximum	1, 120	3, 70	1, 120
Number of centres involved in internal pilot	n	88	–	88
	Mean (SD)	9.4 (11.6)	–	9.4 (11.6)
	Median (IQR)	6.0 (4.0, 12.0)	–	6.0 (4.0, 12.0)
	Minimum, maximum	1, 100	–	1, 100
Proportion of centres used in internal pilot (%)	n	86	–	86
	Mean (SD)	56.8 (31.3)	–	56.8 (31.3)
	Median (IQR)	49.0 (33.3, 100.0)	–	49.0 (33.3, 100.0)
	Minimum, maximum	9.5, 100	–	9.5, 100

IQR interquartile range, SD standard deviation