Cross sectional studies: criteria considered for classification
| (a) Exposure assessment: |
| At least two exposure surrogates were used—for example, (1) duration of exposure and (2) intensity, frequency, or probability of exposure |
| Influence of misclassifications assessed or at least discussed |
| (b) Main outcome measures: |
| Definition of the type of immunoglobulins determined for assessing seroprevalence |
| Definition of the term “clinical” hepatitis A |
| (c) Biases: |
| Exclusion of vaccinated people1-150 |
| Distinction between hepatitis A occurring before and after beginning of employment |
| (d) Confounding factors: |
| At least consideration of the three following variables: age, travelling in endemic areas, socioeconomic status |
| (defined according to education, income, or another recognised classification system) |
| If present consideration of locally important confounding factors—for example, consumption of shellfish |
| (e) Control group: |
| The selection and the composition of the control group must exclude important flaws capable of introducing a bias |
↵1-150 If no information on vaccination could be found, the period during which the study was conducted—or if not indicated the year of publication—was used as an indicator of the probability of vaccination. A vaccination was considered as very unlikely if the study was performed before 1992.