A Decade of Change in Sample Size and Study Setting in Leading Anesthesiology Journals: A Cross-Sectional Meta-Research Study

Background Sample size and study setting are central to the reliability and generalizability of clinical research findings. Clarifying how these design characteristics have changed over time in randomized controlled trials (RCTs) and cohort studies is essential for aligning future anesthesiology research with evolving methodological standards. Methods We reviewed original research articles published in 2014 and 2024 in three leading anesthesiology journals: the British Journal of Anaesthesia (BJA), Anesthesiology, and Anesthesia & Analgesia (A&A). Eligible studies included RCTs and comparative cohort studies of adult patients reporting an effect estimate with a 95% confidence interval. Sample size and the number of participating institutions were extracted. Study setting was classified as single-center or multicenter for RCTs and as single-center, multicenter, or database study for cohort studies. Results Among 415 screened articles, 320 met the inclusion criteria (190 from 2014 and 130 from 2024). The overall median sample size increased significantly from 132.5 (interquartile range {IQR}, 60-720) in 2014 to 1,950.5 (IQR, 133-38,338) in 2024 (P < 0.001). Median sample size increased from 80 to 120 in RCTs (P = 0.013) and from 458 to 6,617 in cohort studies (P < 0.001). The proportion of single-center RCTs did not change significantly (P = 0.55), whereas cohort studies showed a significant decrease in single-center settings (from 70.8% to 46.9%) and an increase in database studies (from 15.1% to 34.7%) (P = 0.001). Conclusions Studies published in 2024 showed substantially larger sample sizes than those in 2014, with cohort studies showing a marked shift toward database studies. These trends may inform the design and planning of future high-impact research in anesthesiology.