Table 2

Risk of bias assessment based on Newcastle-Ottawa Scale

Author Year
CountryNewcastle-Ottawa Scale items addressing different methodological components of the study and potential sources of bias
Representativeness of the exposed cohortSelection of the non-exposed cohortAscertainment of exposureOutcome of interest was not present at start of studyComparability of cohorts on the basis of the design/analysis (confounding)Assessment of outcome blind/record linkageFollow-up long enough for outcome to occurAdequacy of follow-up of cohorts (attrition)
Pruchno et al 199050USA✗*
Vitaliano et al 199344USA
Wright 199442USA
Markiewicz et al 199749Canada
Bannister et al 199845UK
Wells and Over 199847Australia
Wright et al 199843USA
Caron et al 199936USA
Fisher and Lieberman 199939USA
Torossian and Ruffins 199948USA
Spruytte et al 200138Belgium
Burgener and Twigg 200220USA
de Vugt et al 200446Netherlands
McClendon et al 200451USA
Stevens et al 200440USA
Perren et al 200741Switzerland
Kunik et al 2010 (four papers)32–35USA✗*
Clare et al 201437UK
Shroff 201552USA
Snyder 201653USA✗*
  • ✓=study dealt with this adequately. ✗=study was at risk of bias in this area, or provided no information to demonstrate otherwise.

  • *These studies adjusted for three out of the four key confounders.