Table 2

Detailed summary of critical appraisal of included studies using the Newcastle Ottawa Scale (NOS) for assessing the quality of non-randomised control trials (cross-sectional/cohort and case–control studies)

Study, countryNOS quality assessment for studies included (cross-sectional studies/cohort studies)
SelectionComparabilityOutcome
Representativeness of the sampleSelection of the non-exposed cohortAscertainment of exposureDemonstration that outcome of interest was not present at study startComparability of the groups on the basis of design or analysisAssessment of outcomeAdequacy of follow-up of cohortsWas follow-up long enough for outcomes to occurOverall quality assessment score (maximum of 9)Quality (high, medium, low)
Applegate et al66
USA n=1226
*****5Medium quality
Rechardt et al42
Finland n=6237
*****5Medium quality
Rechardt et al43
Finland
n=163
*****5Medium quality
Judge et al68
France
n=147
*1Low quality
NOS quality assessment for studies included (case–control studies)
SelectionComparabilityExposure
Is the case definition adequate?Representativeness of the casesSelection of controlsDefinition of controlsComparability of cases or controls on the basis of design or analysisAscertainment of exposureSame method of ascertainment for cases and controlsNon-Response rate
Abate et al55 Italy
n=180
******6Medium quality
Djerbi et al67 France
n=306
*********9High quality
  • NOS, The Newcastle Ottawa Scale for assessing the quality of non-randomised control trials (cross-sectional/cohort and case–control studies).

  • * and ** are the star rating as per NOS with the study satisfying the item. A study can be awarded a maximum of one star for each numbered item within the Selection and Exposure categories. A maximum of two can be given for Comparability.