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Table 1 Simple regression and multivariate first-order autoregressive models on the number of patients enrolled every quarter.

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

  

All ACTG studies

Excluding substudies

  

Univariate

Multivariate*

Univariate

Multivariate

Parameters

 

Effect (95% CI)

Effect (95% CI)

Effect (95% CI)

Effect (95% CI)

Time trend effect (per quarter)

 

27.1 (18.9, 35.4) ¶

24.5 (17.6, 31.5) ¶

16.1(10.1, 22.1) ¶

14.7 (9.4, 20.2) ¶

Large studies effect ‡ (per point weight)

607.9 (284.5, 931.4) ¶

701.0 (507.7, 894.4) ¶

403.0 (185.6, 20.3) ¶

415.1 (261.0, 569.3) ¶

Early starting effect §

 

-1196.0 (-1858.4,-533.7) ¶

-141.6 (-577.6, 294.3)

-947.4 (-1367.8, -527.0) ¶

-429.2 (-786.9, -47.9) #

Studies starting in same quarter (per study)

59.6 (25.2, 94.0) ¶

31.2 (10.6, 51.8) #

0.7 (-35.9,37.2)

1.6 (-22.0,25.3)

Seasonal effect

     
 

Spring

277.7 (-267.4, 722.8)

126.3 (-89.5, 342.1)

166.9 (-164.4, 498.1)

147.7 (-44.2, 339.5)

 

Summer

136.9 (-358.3, 632.0)

115.5 (-110.4, 341.3)

75.5 (-255.7, 406.7)

41.9 (-150.2, 233.9)

 

Fall

31.0 (-455.2, 517.2)

27.8 (-181.7, 237.2)

21.4 (-303.9, 346.6)

41.8 (-141.5, 225.1)

AR1

  

0.15 (-0.14, 0.45)

 

0.06 (-0.24, 0.35)

  1. ACTG: AIDS Clinical Trials Group, CI: confidence interval AR1: first-order autoregressive parameter * Constant in model = 109.7 (p = 0.47) † Constant in model = 520.3 (p < 0.001) ‡ 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