Risk of bias by year

Quality assessment of the review articles was performed using modified AMSTAR (Burda, Holmer and Noris 20161; Shea et al. 20072) and AMSTAR-2 (Shea et al.20173) checklist. The quality assessment was carried out using 16 quality assessment questions. For more details of these 16 questions, please visit Quality assessment scheme.

Based on the scoring for 16 questions and also based on the subjective overall evaluation of the assessors, an overall rating (Quality Index) was then assigned to each review article, highlighting whether major concerns arose during the quality assessment that may affect overall conclusions of the review article.Then a risk of bias score was assigned to each review article to represent how likely are the main conclusions of the review to be biased.


  1. Burda, B.U., Holmer, H.K. and Norris, S.L., 2016. Limitations of A Measurement Tool to Assess Systematic Reviews (AMSTAR) and suggestions for improvement. Systematic reviews, 5(1), p.58.
  2. Shea, B.J., Grimshaw, J.M., Wells, G.A., Boers, M., Andersson, N., Hamel, C., Porter, A.C., Tugwell, P., Moher, D. and Bouter, L.M., 2007. Development of AMSTAR: a measurement tool to assess the methodological quality of systematic reviews. BMC medical research methodology, 7(1), p.10.
  3. Shea, B.J., Reeves, B.C., Wells, G., Thuku, M., Hamel, C., Moran, J., Moher, D., Tugwell, P., Welch, V., Kristjansson, E. and Henry, D.A., 2017. AMSTAR 2: a critical appraisal tool for systematic reviews that include randomised or non-randomised studies of healthcare interventions, or both. bmj, 358, p.j4008.

The following diagram illustrate the distribution of risk of bias among different publication years.