Table 1.

Risk of bias classification by which studies were assessed, adopted directly from Hoy et al. [32] overall judgements are shown in Table 2

Domain	Question
External validity
D1	Was the target population a close representation of the national population?
D2	Was the sampling frame a true or close representation of the target population?
D3	Was some form of random selection used to select the sample, or was a census undertaken?
D4	Was the likelihood of response bias minimal?
Internal validity
D5	Were data collected directly from subjects?
D6	Was an acceptable case definition used in the study?
D7	Was the study instrument that measured the parameter of interest shown to have validity and reliability?
D8	Was the same mode of data collection used for all subjects?