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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