Background: For scientific and ethical reasons randomized controlled clinical trials (RCTs) should be based on a sample size calculation. The CONSORT statement, an established publication guideline for transparent study reporting, requires a sample size calculation in every study publication.
Objective: The availability of sample size calculations in RCT publications on treatment of age-related macular degeneration (AMD) was investigated. The primary hypothesis of this investigation compared the prevalence of reported sample size calculations between journals with higher (≥5) versus lower (<5) impact factors (IF).
Material and methods: It was examined whether information on sample size calculation was available in a series of 97 publications of RTCs on AMD treatment published between 2004 and 2014.
Results: Only 46 out of 97 (47%) study publications provided information on the reason for the number of patients enrolled. The comparison of publications from journals with an IF ≥ 5 (63%, 30) and from journals with an IF < 5 (40%, 67) showed a statistically significant difference of 23% in the frequencies of available sample size calculations (95% confidence interval, CI 2%; 44%). Of the publications published before 2010, 43% reported a sample size calculation versus 51% of the publications afterwards.
Conclusion: Publications in journals with higher IF more frequently reported a sample size calculation. More than 50% of the publications did not report any sample size calculation. Authors and reviewers of publications should pay more attention to the explicit reporting of sample size calculations.
Keywords: CONSORT statement; Clinical trials; Quality of publications; Study planning; Transparent reporting.