risk of bias assessment in non-randomized studies of interventions for premenstrual syndrome: a systematic review

Objective: premenstrual syndrome (pms) is a very prevalent condition that affects premenopausal women and can result in monthly debilitating emotional and physical symptoms. the objective of this systematic review was to determine which predictive factors were associated with an increased amount of bias in non-randomized studies (nrss) of pms. materials and methods: a search of the embase and medline electronic databases was completed from january 1, 2010 to december 2021. the methodological quality of the included studies was independently evaluated and critically appraised using the risk of bias in non-randomized studies - of interventions (robins-1) tool. associations of different factors with the risk of bias levels were assessed using a univariate logistic regression. odds ratio and 95% confidence interval (ci) were reported. results: of the 1668 studies, 38 were determined to be eligible for inclusion. the robins-1 tool identified that 12 studies were of low/moderate risk of bias (31.6%) and 26 were of serious/critical risk (68.4%). evidence of relationships between the robins-1 score and impact factor (or=0.20; 95% ci, 0.07 to 0.57; p= 0.003) and number of authors (or=0.65; 95% ci, 0.43 to 0.99; p= 0.046) were identified, whereas no relationships were found with the number of citations, the sample size, the funding type, or the conflict-of-interest statement. conclusion: the systematic review concludes that the methodological rigor of non-randomized studies of pms can vary, with fewer authors and a lower impact factor showing evidence of association with a decreased quality of evidence.