Publication bias in randomized controlled trials in dentistry. What factors affect statistical significance of outcomes?

Abstract

Objectives: To record the proportion of Randomized Controlled Trials (RCTs) reporting significant (versus non- significant) primary outcomes, published across 12 high impact journals in Dentistry, covering 6 specialty domains. Associations with certain journal, publication and outcome characteristics were examined.

Methods: We identified and included all RCTs published from January 1st, 2017 to December 31st, 2021 in the two journals with the highest impact factors (Clarivate Analytics, 2020) from each of the following domains: Periodontology, Endodontics, Restorative Dentistry/ Prosthodontics, Orthodontics, Paediatric Dentistry, Oral and Maxillofacial Surgery. The primary outcome was the proportion of significant/ non- significant findings reported for the primary outcomes under study, while a range of characteristics such as: journal, year of publication, impact factor, funding, registration and others, were tested for associations.

Results: A total of 474 RCTs were identified and included, with the majority reporting statistically significant outcomes (321/474; 67.7%). The multivariable model revealed significant effects of predictors related to specialty domain (p = 0.01), continent (p = 0.003) and registration (p = 0.004). Compared to Periodontology, RCTs published in Endodontics (OR= 0.40; 95%CIs: 0.22, 0.76) and Orthodontics (OR= 0.41; 95%CIs: 0.23, 0.74) were less likely to present statistically significant effects. There was strong evidence that registered trials presented lower odds of reporting statistically significant findings (OR= 0.52; 95%CIs: 0.34, 0.81).

Conclusions: The entirety of dentistry domains demonstrated preferential publication practices of outcomes considered as "successful" and statistically significant, with domains such as Orthodontics and Endodontics being more balanced. Trial non- registration is still prevalent and associated with reporting of statistically significant effects.

Clinical significance: The findings of this empirical report bring attention to the interpretation of Systematic Reviews (SRs) conclusions. These largely depend on the availability and nature of outcomes of randomized controlled trials (RCTs) on a topic, which may impact on the synthesized estimate of a pooled effect and its direction.

Keywords: Dentistry; Publication bias; RCT; Randomized controlled trials; Statistical significance.