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Table 4 Reported rates of participant flow through the trial as a percentage of the number required by the reported sample size calculation

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

  Number of studiesa Median % of sample size required First and third quartiles Minimum and maximum
Invited to screening 12 410% 288%, 951% 131%, 2549%
Attend screening 62 230% 132%, 379% 83%, 2361%
Eligible 58 130% 108%, 160% 72%, 431%
Randomised 106 110% 100%, 128% 43%, 213%
Outcome assessed 94 100% 92%, 111% 36%, 158%
In analysis 102 103% 98%, 117% 43%, 169%
  1. 7 studies which stopped early having demonstrated a benefit of treatment are excluded from these analyses
  2. a Relates to the number of studies providing relevant data
  3. Note: the α (significance) and 1-β (power) levels used in each trial's sample size calculation may vary
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