Masarwa R, et al. - Researchers sought to assess the role of potential unmeasured confounding in the estimation of the correlation between acetaminophen usage during pregnancy and the risk of attention deficit hyperactivity disorder (ADHD), through bias analysis. Further, they determine the roles of selection bias and exposure misclassification. They searched MEDLINE, Embase, Scopus, and the Cochrane Library up to December 2018, which involved observational studies examining the correlation among acetaminophen usage during pregnancy and the risk of ADHD. In a meta-analysis, seven studies were involved. Overall, bias analysis implies that unmeasured confounding might explain the earlier reports of correlation of acetaminophen usage during pregnancy with an increased risk of ADHD in the offspring.