Background

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 RCTs. This study assessed evidence of highly unusual distributions of baseline characteristics of subjects enrolled in clinical trials in implant dentistry.

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

1538 unique RCTs were identified. 409 (26.6%) did not report baseline characteristics of the population. 671 (43.6%) reported data in forms other than mean and standard deviation and could not be used to assess their random sampling. 458 trials with 1449 baseline variables in forms of mean and standard deviation were assessed. The study observed an over-representation of very small P values (<0.001, 1.38%, 95% 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-center RCTs.

Conclusions

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, 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.

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