Systematic review of sample size calculations and reporting in randomized controlled trials in ophthalmology over a 20-year period

Abstract

Purpose: Randomized Controlled Trials (RCTs) are considered the gold standard for the practice of evidence-based medicine. The purpose of this study is to systematically assess the reporting of sample size calculations in ophthalmology RCTs in 5 leading journals over a 20-year period. Reviewing sample size calculations in ophthalmology RCTs will shed light on the methodological quality of RCTs and, by extension, on the validity of published results.

Methods: The MEDLINE database was searched to identify full reports of RCTs in the journals Ophthalmology, JAMA Ophthalmology, American Journal of Ophthalmology, Investigative Ophthalmology and Visual Science, and British Journal of Ophthalmology between January and December of the years 2000, 2010 and 2020. Screening identified 559 articles out of which 289 met the inclusion criteria for this systematic review. Data regarding sample size calculation reporting and trial characteristics was extracted for each trial by independent investigators.

Results: In 2020, 77.9% of the RCTs reported sample size calculations as compared with 37% in 2000 (p < 0.001) and 60.7% in 2010 (p = 0.012). Studies reporting all necessary parameters for sample size recalculation increased significantly from 17.2% in 2000 to 39.3% in 2010 and 43.0% in 2020 (p < 0.001). Reporting of funding was greater in 2020 (98.8%) compared with 2010 (89.3%) and 2000 (53.1%). Registration in a clinical trials database occurred more frequently in 2020 (94.2%) compared to 2000 (1.2%; p < 0.001) and 2010 (68%; p < 0.001). In 2020, 38.4% of studies reported different sample sizes in the online registry from the published article. Overall, the most studied area in 2000 was glaucoma (29.6% of RCTs), whereas in 2010 and 2020, it was retina (40.2 and 37.2% of the RCTs, respectively). The number of patients enrolled in a study and the number of eyes studied was significantly greater in 2020 compared to 2000 and 2010 (p < 0.001).

Conclusion: Sample size calculation reporting in ophthalmology RCTs has improved significantly between the years 2000 and 2020 and is comparable to other fields in medicine. However, reporting of certain parameters remains inconsistent with current publication guidelines.

Keywords: RCTs; Randomized clinical trials; Sample size; Sample size calculation; Sample size reporting.