Abstract
OBJECTIVE: The purpose of this study was to describe sample size calculations in randomized clinical trials (RCTs) published in four orthodontic journals. METHODS: This cross-sectional study evaluated 142 RCTs published from 2015 to 2019 in the four journals with the highest impact factor in orthodontics according to SCIMAGO 2018 ranking. Two trained and experienced orthodontists assessed if the RCTs evaluated reported their sample size calculations, and if they adequately described the criteria for the calculations, including the level of significance, test power, precision or effect size (clinically relevant difference), and expected variability. The reporting of sample size calculation was considered adequate when the above four criteria were described. RESULTS: We identified 120 publications (84.5%) reporting the sample size calculation, but only 70 (58.3%) fully described the above parameters. Inadequate calculation included failure to report the confidence level (ranging from 0% to 12.9%), test power (ranging from 0% to 20%), effect size (ranging from 0% to 22.5%) and expected variability (ranging from 22.6% to 80%). According to the journal, some parameters of sample size calculation were more frequently reported. CONCLUSION: RCTs published in four leading orthodontic journals frequently do not report the parameters used for sample size calculations.