Table 3

Risk of bias assessment

External validityProctor and Boan-LenzoStorch et alBrand et alGhaedi et alJunge and Feddermann-Demont
 1. Were the study’s target populations a close representation of relevant populations in relation to relevant variables?YesYesYesYesYes
 2. Was the sampling frame a true or close representation of the target population?YesYesYesYesYes
 3. Was some form of random selection used to select the sample, or was a census undertaken?NoNoNoNoNo
 4. Was the likelihood of non-response bias minimal?UnclearUnclearUnclearUnclearUnclear
Internal validity
 5. Were data collected directly from the subjects (as opposed to a proxy)?YesYesYesYesYes
 6. Was an acceptable case definition used in the study?YesYesYesYesYes
 7. Was the study instrument that measured the parameter of interest shown to have validity and reliability?YesYesYesYesYes
 8. Was the same mode of data collection used for all subjects?YesYesYesYesNo
 9. Was the length of the shortest prevalence period for the parameter of interest appropriate?YesYesYesYesYes
 10. Were the numerator(s) and denominator(s) for the parameter of interest appropriate?YesYesYesYesYes