A detailed commentary on the major methodological problems or biases that affected the studies is also included, together with a description of how this in our judgement has affected the individual study results.
Available evidence is scarce and frequently associated with major methodological flaws and confirmation bias.
Based on our experience as ophthalmologists, the major methodological issue that may cause a bias is, to our opinion, the way the assessment of the visual acuity was conducted.
Moreover, many of these studies suffer from major methodological shortcomings, including small sample sizes, referral biases, high loss to follow-up, inadequate matching of groups, and lack of gender inclusion and analysis [ 9, 10, 12].
The study of weak associations magnifies the three major methodological problems faced by observational research: chance, bias, and confounding.
Therefore, the majority of published G × E studies have suffered from lack of replication, low-power, a publication bias towards positive results and major methodological concerns (for a critical review see Duncan & Keller, 2011).
The bias introduced by the JIF arises directly from the major methodological problems raised against using citation analysis to evaluate journals.
The major methodological concern in observational studies on medical interventions, including transfusion, is the obvious risk of bias due to confounding; this is also the case in our study.
Many methodological biases preclude conclusive information.
There were few patients and methodological biases were numerous.
