Registry versus publication: discrepancy of primary outcomes and possible outcome reporting bias in child and adolescent mental health.

Outcome reporting bias is one of the fundamental forms of publication bias. It implies publishing only outcomes that have positive results. The aim of this observational study was to explore primary outcome discrepancies between registry of clinical trials and their corresponding publications, since these can indicate outcome reporting bias in child mental health. Data were extracted from completed interventional clinical trials from ClinicalTrial.gov registry and its Archive site. Trials were registered under "Behaviours and Mental Disorders" category, and conducted on underage participants (0-17 years). Their primary outcomes were compared to those published in publication which had a corresponding NCT number stated in the text. Sixteen percent of trials did not have the minimum information on primary outcome stated in the registry-neither the measure used nor the measurement time points; 38.9% of trials had the minimum information stated to describe primary outcome, while only 3.3% of trials had all the necessary elements stated in the registry. Most of the publication in our sample had positive results (66.4%). Half of the trials registered before completion had non-matching primary outcomes in the registry and publication; 85.4% of trials with non-matching outcomes indicated possible outcome reporting bias for some of the primary outcome. Middle-sized trials and industry-funded trials were related with higher quality of primary outcome registration. Industry funding was related with positive findings in publication. Non-industry funding proved to be the only significant predictor of discrepancy between registered and published primary outcomes, and possible outcome reporting bias. Journal impact factor was not related with any of the outcome measures. The main limitation of the study is that it primarily offers an insight into discrepancy of registered and published outcomes. The methodology does not imply an access to results of unpublished outcomes - therefore, it was not possible to determine the presence of the bias with sufficient certainty in large number of trials. Further research should be done with improved methodology and additional data.