Evidence and risk indicators of non‐random sampling in clinical trials in implant dentistry: A systematic appraisal

AIM: Analysis of distribution of p‐values of continuous differences between test and controls after randomization provides evidence of unintentional error, non‐random sampling, or data fabrication in randomized controlled trials (RCTs). We assessed evidence of highly unusual distributions of baseline characteristics of subjects enrolled in clinical trials in implant dentistry. MATERIALS AND METHODS: RCTs published between 2005 and 2020 were systematically searched in Pubmed, Embase, and Cochrane databases. Baseline patient data were extracted from full text articles by two independent assessors. The hypothesis of non‐random sampling was tested by comparing the expected and the observed distribution of the p‐values of differences between test and controls after randomization. RESULTS: One‐thousand five‐hundred and thirty‐eight unique RCTs were identified, of which 409 (26.6%) did not report baseline characteristics of the population, and 671 (43.6%) reported data in forms other than mean and standard deviation and could not be used to assess their random sampling. Four‐hundred and fifty‐eight trials with 1449 baseline variables in the form of mean and standard deviation were assessed. The study observed an over‐representation of very small p‐values [<.001, 1.38%, 95% confidence interval (CI) 0.85–2.12 compared to the expected 0.10%, 95% CI 0.00–0.26]. No evidence of over‐representation of larger p‐values was observed. Unusual distributions were present in 2.38% of RCTs and more frequent in non‐registered trials, in studies supported by non‐industry funding, and in multi‐centre RCTs. CONCLUSIONS: The inability to assess random sampling due to insufficient reporting in 26.6% of trials requires attention. In trials reporting suitable baseline data, unusual distributions were uncommon, and no evidence of data fabrication was detected, but there was evidence of non‐random sampling. Continued efforts are necessary to ensure high integrity and trust in the evidence base of the field.