Table 4. Summary score for methodological quality of repeated cross-sectional studies.

Study ID	Q1	Q2	Q3	Q4	Q5	Q6	Q7	Q8	Total of ‘yes’ scores
Mahendra et al. 2006 [63]	Y	Y	Y	Y	N	N	Y	Y	6

NB: Y = Yes, U = unclear, NA = not applicable

Q1. Were the criteria for inclusion in the sample clearly defined?

Q2. Were the study subjects and the setting described in detail?

Q3. Was the exposure measured in a valid and reliable way?

Q4. Were objective, standard criteria used for measurement of the condition?

Q5. Were confounding factors identified?

Q6. Were strategies to deal with confounding factors stated?

Q7. Were the outcomes measured in a valid and reliable way?

Q8. Was appropriate statistical analysis used?