The need to rapidly spread information about the risk of COVID-19 in patients with psoriasis (Pso) and psoriatic arthritis (PsA) on biologics may have hampered the methodological rigor in published literature. We analysed the quality of papers dealing with the risk and outcomes of COVID-19 in patients with Pso and PsA receiving biologic therapies. The Newcastle-Ottawa Scale (NOS) was used to estimate the quality of the published studies. Moreover, to better contextualize results, specific internal and external validity items were further considered, i.e. case definition, modality of COVID-19 assessment, evidence for self-selection of participants, percentage of dropout/nonparticipants, and sample size calculation. Twenty-five out of 141 papers were selected. The median NOS score was 47% for Pso and 44% for PsA, indicating an overall high risk of bias. 37% of Pso and 44% of PsA studies included patients with suspected COVID-19 without a positive swab. No studies provided a formal sample size calculation.
A significant risk of bias in all the published papers was found. Major issues to be considered in future studies are: reduction of ascertainment bias, better consideration of non-response or participation bias, and provision of formal statistical power calculation .