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Table 6 Comparing the ability to recruit to the target the number of participants between cRCTs and iRCTs using results of previous studies that reviewed iRCTs

From: Statistical analysis of publicly funded cluster randomised controlled trials: a review of the National Institute for Health Research Journals Library

Review McDonald et al. Sully et al. Walters et al. This study
Recruitment period 1994–2002 2002–2008 2004–2016 1997–2021
Number of trials in the study N = 122 iRCTs N = 73 iRCTs N = 151 iRCTs N = 86 cRCTs
Recruited 100% of original target 38 of 122 (31%) 40 of 73 (55%) 61 of 151 (40%) 57 of 86 (66%)
Original target was revised 42 of 122 (34%) 14 of 73 (19%) 52 of 151 (34%) 21c of 86 (24%)
Original target revised upward 6 of 42 (14%) 5 of 14 (36%) 11 of 52 (21%) 12 of 21 (57%)
Original target revised downward 36 of 42 (86%) 9 of 14 (64%) 41 of 52 (79%) 9 of 21 (43%)
Recruited 80% of original target 67 of 122 (55%) 57 of 73 (78%) 95 of 151 (63%) 71 of 86 (83%)
Recruited 100% of revised target 19 of 42 (45%) 10 of 14 (71%) 28 of 52 (54%) 16 of 21 (76%)
Recruited 80% of revised target 34 of 42 (80%) 13 of 14 (93%) 48 of 52 (92%) 21 of 21 (100%)
Extended their recruitment 65 of 122 (54%) 33 of 73 (45%) 49 of 151(32%) 11 of 86 (13%)
  1. Source: Adapted (and modified) from Walters et al. [16]
  2. cWas supposed to be 25 trials but 2 trials did not report their original target that was revised, and another two trials did not report their final revised target and the number of participants recruited respectively; they were excluded since comparison cannot be done