Determinants of patient recruitment in a multicenter clinical trials group: trends, seasonality and the effect of large studies

Table 2 Training model based on the first 32 quarters of enrollment

		All ACTG studies	Excluding substudies
Parameters		Effect (95% CI)	Effect (95% CI)
AR1		0.04 (-0.37, 0.46)	-0.09 (-0.51, 0.33)
Time trend effect		29.7 (18.9, 40.5) ‡	12.8 (3.9, 21.7) §
(per quarter)
Large studies effect ^*(per point weight)		699.7 (535.5, 864.0) ‡	420.3 (284.2, 556.4) ‡
Early starting effect †		-83.3 (-427.3, 260.7)	-436.7 (-731.1,-142.2) §
Studies starting in same quarter (per study)		20.6 (-1.4, 42.5)	-1.0 (-23.5, 21.4)
Seasonal effect
	Spring	152.7 (-78.8, 406.2)	189.3 (-32.4, 410.9)
	Summer	185.3 (-43.2, 413.7)	115.3 (-90.6, 321.2)
	Fall	-144.5 (-365.2, 76.2)	-96.7 (-308.8, 115.4)
Constant		137.5 (-152.2, 427.2)	576.5 (309.3, 843.7) ‡

ACTG: AIDS Clinical Trials Group, AR1: First-order autoregressive parameter ^* Sum of weights for large studies in each quarter: ½ for a large study which is initiated in that quarter, 1 for a large study which is on its second quarter of enrollment, and ½ for a large study which is on its third quarter of enrollment. † Dummy variable for first 3 quarters (Fall 1986-Spring 1987) ‡ p < 0.001 §0.001 ≤ p < 0.05