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

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

   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) ‡
  1. 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