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Table 3 Planned participants and clusters recruitment to targets in cluster trials

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

Characteristics n % Mean (SD) Median Range IQR
Original individual participant target sample size (N = 84b)
≤ 300 11 13 10,035 (31357) 1250 136–250,000 550–4466
301–600 11 13     
601–900 13 15     
901–1200 3 4     
1201–1500 11 13     
1501–1800 3 4     
> 1800 29 35     
Not reported 3 3     
Final individual participant target sample size (N = 84b)
≤ 300 11 13 9372 (30173) 1212 136–250,000 534–4258
301–600 11 13     
601–900 14 17     
901–1200 5 6     
1201–1500 11 13     
1501–1800 3 4     
> 1800 27 32     
Not reported 2 2     
Original individual participant target sample size met (N = 86)
Yes 57 66     
No, but >= 80% met 14 16     
No and < 80% met 9 11     
Final individual participant recruitment target met (N = 86)
Yes 58 67     
No, but 80% >= of target met 17 20     
No and < 80% of target met 6 7     
Not reported 5 6     
Revised original individual participant target sample size (N = 86)
Yes, upward 13 15     
Yes, downward 9 10     
Yes, direction not reported 4 4     
No 61 71     
Original cluster recruitment target met (N = 86)
Yes 68 79     
No, but >= 80% met 9 11     
No, and < 80% met 1 1     
Not reported 8 9     
  1. bTwo studies were excluded because the original and final targets were expressed in person-years of observation and not specific number of participants [41, 54]. N = total number of trials; n = counts observed in each level of a variable; SD = standard deviation; IQR = interquartile range. Not reported means that the information of interest was not considered and/or provided in the trial