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Table 2 Sample size calculations for the three primary outcome measures assuming an 11% reduction in error rates for the simple feedback group and a 50% reduction in error rates for the intervention group

From: Protocol for the PINCER trial: a cluster randomised trial comparing the effectiveness of a pharmacist-led IT-based intervention with simple feedback in reducing rates of clinically important errors in medicines management in general practices

Outcome measure Patients with a history of peptic ulcer who have been prescribed a non-selective NSAID Patients with asthma who have been prescribed a beta-blocker Patients aged 75 years and older prescribed an ACE inhibitor or a loop diuretic long-term without a check of their renal function and electrolytes in the previous 15 months
Median error rate1
(Interquartile range)
(3.76% – 7.85%)
(1.27% – 3.08%)
(15.13% – 32.69%)
Error rate in control group (assuming 11% reduction) 5.13% 1.69% 17.62%
Error rate in intervention group (assuming 50% reduction) 2.88% 0.95% 9.90%
Intraclass Correlation Coefficient (ICC)1 0.01082 0.00657 0.00952
Cluster size1 63 439 105
Inflation factor 1.7 3.9 2.0
Total number of practices required 64 66 12
  1. 1 Estimated using data obtained from 43 general practices contributing to the QResearch database