TABLE 1

Results of Risk-of-Bias Assessment for Cohort Studies

Cohort StudiesaOverall Risk-of-Bias scoreRisk of BiasbCriteria
SelectionComparabilitycOutcome
Representativeness of the Exposed CohortSelection of the Nonexposed CohortAscertainment of CasesOutcome of Interest Was Not Present at Start of StudyComparability of the Design and Analysis for CohortsAssessment of OutcomeSufficient Follow-up DurationAdequacy of Follow-up of Cohorts
van Santen et al33 (2013)6 of 9HighXXXXXX
Ludvigsson et al34 (2015)8 of 9LowXXXXXXXX
van der Maas et al35 (2016)7 of 9HighXXXXXXX
Fell et al36 (2016)8 of 9LowXXXXXXXX
Zerbo et al37 (2017)7 of 9HighXXXXXXX
Hviid et al38 (2017)8 of 9LowXXXXXXXX
Walsh et al39 (2019)8 of 9LowXXXXXXXX
  • a Cohort studies were assessed using the Newcastle–Ottawa scale. Each X represents whether an individual criterion is satisfied. Each — represents whether an individual criterion is not satisfied.

  • b Low risk of bias: overall risk of bias score ≥8; high risk of bias: overall risk of bias score <8.

  • c All criteria receives a maximum score of 1 X except for comparability of study groups where an additional X may be allocated for the control of additional important confounders.30