Table 2

Risk of bias and quality assessment for prevalence studies14

ItemsQuality score
External validity
1. Was the study’'s target population a close representation of the national population in relation to relevant variables?(1 point)
2. Was the sampling frame a true or close representation of the target population?(1 point)
3. Was some form of random selection used to select the sample, or was a census undertaken?(1 point)
4. Was the likelihood of non-response bias minimal?(1 point)
Total(4 points)
Internal validity
1. Were data collected directly from the participants (as opposed to a proxy)?(1 point)
2. Was an acceptable case definition used in the study?(1 point)
3. Was the study instrument that measured the parameter of interest shown to have validity and reliability?(1 point)
4. Was the same mode of data collection used for all participants?(1 point)
5. Was the length of the shortest prevalence period for the parameter of interest appropriate?(1 point)
6. Were the numerator(s) and denominator(s) for the parameter of interest appropriate?(1 point)
Total(6 points)