Table 2:

Risk of bias assessment using the modified Newcastle–Ottawa Scale

InvestigatorSelection bias: is source population representative?Performance biasDetection biasInformation biasTotal score*
Is sample size sufficient, is there sufficient power?Did study adjust for confounders?Did study use appropriate statistical analysis?Are there few missing data, was this handled appropriately?Outcome measurement appropriate?Objective assessment of outcome of interest?
Bell et al.48223322216
Best et al.30232112011
Bleich et al.4411011138
Epstein et al.31010323312
Joe et al.39333323320
Levine et al.32222213315
Lions et al.33120213211
Nava et al.3401021239
Nirenberg et al.35210113311
Peirce et al.45133333319
Peles et al.40333333321
Peles et al.41333333321
Proctor et al.36333113317
Saxon et al.4611011239
Saxon et al.37223222316
Scavone et al.13113121211
Schiff et al.42332323319
Somers et al.38211121311
Strain et al.4720012218
Wasserman et al.43203333317
Weizman et al.43222111312
White et al.17230122313
Zielinski et al.14333312318
  • * 0 = definitely no (high risk of bias), 1 = mostly no (met a little of the criterion), 2 = mostly yes (met most of the criterion), 3 = definitely yes (low risk of bias). Maximum total score 21.