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Table 5 Associations between recruitment and retention rates and trial characteristics

From: A review of reporting of participant recruitment and retention in RCTs in six major journals

  Screened and eligible Eligible and randomised Randomised and outcome assessed
Factor & level Median IQR Number of studies Median IQR Number of studies Median IQR Number of studies
Study size          
<200 78 63, 95 25 90 79, 100 26 92 86, 94 32
200–449 71 56, 95 18 93 78, 99 21 92 86, 99 29
450–749 51 33, 64 15 86 66, 97 15 93 84, 98 23
750+ 71 41, 80 13 91 85, 100 13 97 89, 100 29
    p = 0.026    p = 0.99    p = 0.24
Number of arms          
2 72 48, 93 56 90 78, 100 59 94 88, 99 89
3+ 68 51, 79 15 89 70, 97 16 86 76, 94 24
    p = 0.33    p = 0.75    p = 0.0035
Multi-centre?          
Yes 75 42, 86 44 92 73, 99 47 94 85, 99 79
No 64 50, 94 27 87 78, 100 28 93 88, 96 34
    p = 0.91    p = 0.70    p = 0.64
Treatment focus          
Drug 71 53, 86 29 94 73, 100 30 94 86, 99 56
Surgery 75 48, 99 10 89 63, 100 10 99 92, 100 17
Allied 67 50, 88 17 91 81, 99 18 90 85, 94 18
Other 64 44, 86 15 86 79, 93 17 92 84, 96 22
    p = 0.89    p = 0.56    p = 0.014
Control          
Active 70 51, 86 30 88 74, 95 32 92 85, 98 52
Placebo 68 49, 88 41 94 77, 100 43 93 86, 99 61
    p = 0.82    p = 0.24    p = 0.46
Time to assessment          
0 to 4 weeks 8 33, 86 10 83 63, 94 11 99 93, 100 26
>4 weeks to 6 months 7 51, 78 23 91 81, 100 24 92 87, 94 30
>6 to 18 months 74 40, 93 20 94 72, 99 21 88 79, 98 31
>18 months 75 63, 93 16 91 83, 100 16 95 86, 100 23
    p = 0.087    p = 0.242    p = 0.075
Funding          
Pharma 74 54, 93 28 94 83, 100 29 93 85, 99 56
Government/charity 67 48, 86 38 85 70, 97 40 93 86, 96 49
Internal/unstated 56 51, 56 5 98 94, 100 6 95 91, 100 8
    p = 0.51    p = 0.048    P = 0.50
  1. P values were obtained from Mann-Whitney tests (for characteristics with two levels), Kruskal-Wallis tests (three or more unordered levels) or trend tests (three or more ordered levels)
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