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Table 3 Variation in cluster sizes (number of eligible participants per general practice) in two cluster randomized trials in CPRD

From: Cluster randomized trials utilizing primary care electronic health records: methodological issues in design, conduct, and analysis (eCRT Study)

Trial

Estimate

Antibiotic trial

 

Participants

Registered adults aged 18 to 59 years

Cluster size (median, IQR)

5,246 (3,608 to 7,219)

Minimum cluster size

811

Maximum cluster size

16,984

Mean (SD) cluster size

5,588 (2,938)

CV of cluster sizes

0.53

Stroke trial

 

Participants

Patients with prevalent stroke

Cluster size (median, IQR)

102 (60 to 148)

Minimum cluster size

19

Maximum cluster size

343

Mean (SD) cluster size

110 (62)

CV of cluster sizes

0.56

  1. CV, Coefficient of variation; IQR, Interquartile range; SD, Standard deviation.