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

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

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%)	21^c 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%)

Source: Adapted (and modified) from Walters et al. [16]
^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

ISSN: 1745-6215