Journal of Advances in Medicine and Medical Research

Aims: A realistic sample size calculation is an essential step in planning a clinical trial. It includes the consideration of the expectable drop out profile during individual patient observation periods to ensure a sufficient sample size for statistical analysis. Aim of this meta-analysis was to estimate dropout rates for randomized controlled trials (RCT) on cataract surgery during a follow–up period of 6 and 12 months in order to optimize sample size calculation.

Methodology: A full text hand search in five ophthalmological journals (publication period 01/2002 – 12/2012) for RCTs on cataract surgery was performed. The meta-estimation of the reported 6 and 12 months drop out rates was based on the random effects model and stratified for the trial design characteristic “comorbidities allowed by design”.

Results: 35 RCTs reporting no comorbidities (total patient count n=3.055) and 9 RCTs reporting comorbidities by design (n=8.631) met the inclusion criteria for the 6 months follow-up evaluation; 41 RCTs without comorbidities (n=3.384) and 7 RCTs allowing for comorbidities (n=1.082) were identified for the 12 months follow-up evaluation. Respective and 12 months meta drop out rates of 7.8% (95% CI 5.0 – 11.8%) and 16.3% (95% CI 13.2 – 20.0%) were estimated from RCTs without comorbidities. RCTs allowing for comorbidity by design demonstrated lower drop out estimates with 3.2% (95% CI 2.9 – 3.6%) after 6 months follow-up and 6.7% (95% CI 3.9 – 11.2%) after 12 months.

Conclusion: Sample size calculation in cataract surgery should account for drop outs rates of at least 10% during a 6 months and of at least 20% during a 12 months follow-up period.