This study aimed to compare the Newcastle-Ottawa Scale (NOS) assessments of risk of bias between reviewers and authors of cohort studies included in a systematic review on risk factors for severe outcomes in influenza patients. The NOS is a tool used to evaluate the quality of observational studies, and its reliability is crucial for generating accurate systematic reviews. The study included 182 cohort studies published between 2008 and 2011, with 65 authors completing the survey. The overall NOS score was significantly higher (p < 0.001) in the reviewers' assessment (median = 6) compared to the authors' (median = 5). Inter-rater reliability was poor, ranging from slight to poor, indicating minimal agreement between reviewers and authors. The findings suggest that the NOS may be subject to high subjectivity, and systematic reviewers should contact authors for additional information not published in the studies to improve the reliability of risk of bias assessments.This study aimed to compare the Newcastle-Ottawa Scale (NOS) assessments of risk of bias between reviewers and authors of cohort studies included in a systematic review on risk factors for severe outcomes in influenza patients. The NOS is a tool used to evaluate the quality of observational studies, and its reliability is crucial for generating accurate systematic reviews. The study included 182 cohort studies published between 2008 and 2011, with 65 authors completing the survey. The overall NOS score was significantly higher (p < 0.001) in the reviewers' assessment (median = 6) compared to the authors' (median = 5). Inter-rater reliability was poor, ranging from slight to poor, indicating minimal agreement between reviewers and authors. The findings suggest that the NOS may be subject to high subjectivity, and systematic reviewers should contact authors for additional information not published in the studies to improve the reliability of risk of bias assessments.