Table 4

Included studies risk of bias

Author	Item 1	Item 2	Item 3	Item 4	Item 5	Item 6	Item 7	Item 8	Item 9	Item 10	Overall risk of bias
Author	External validity				Internal validity						Overall risk of bias
Ayeni et al 40	HR	HR	HR	LR	LR	HR	HR	LR	LR	LR	MR
Dickenson et al 67	HR	HR	HR	LR	LR	HR	LR	LR	LR	HR	MR
Domb et al 55	HR	HR	HR	LR	LR	LR	HR	HR	LR	HR	HR
Farrell et al 59	HR	HR	HR	LR	LR	HR	HR	LR	LR	LR	MR
Georgiadis et al 60	HR	HR	HR	LR	LR	HR	HR	HR	LR	LR	HR
Jayakar et al 61	HR	HR	HR	LR	LR	LR	HR	LR	LR	HR	MR
Ji et al 56	HR	HR	HR	LR	LR	LR	LR	HR	LR	LR	MR
Kassarjian et al 41	HR	HR	HR	LR	LR	LR	HR	LR	LR	HR	MR
Kolo et al 51	HR	HR	HR	LR	LR	LR	HR	LR	LR	HR	MR
Lahner et al 42	HR	HR	HR	LR	LR	HR	HR	LR	LR	LR	MR
Lahner et al 57	HR	HR	HR	LR	LR	HR	HR	LR	LR	HR	HR
Lee et al 64	HR	HR	HR	LR	LR	LR	LR	LR	LR	LR	LR
Leunig et al 52	HR	HR	LR	LR	LR	LR	LR	LR	LR	LR	LR
Mayes et al 58	HR	HR	HR	LR	LR	LR	LR	LR	LR	LR	LR
Mayes et al 43	HR	HR	HR	LR	LR	LR	LR	LR	LR	LR	LR
Mayes et al 65	HR	HR	HR	LR	LR	LR	LR	LR	LR	LR	LR
Mineta et al 62	HR	HR	HR	LR	LR	LR	LR	LR	LR	HR	MR
Narvani et al 44	HR	HR	HR	LR	LR	HR	HR	LR	LR	LR	MR
Neiman et al 63	HR	HR	HR	LR	LR	HR	HR	LR	LR	LR	MR
Neumann et al 45	HR	HR	HR	LR	LR	LR	HR	LR	LR	LR	MR
Panzer et al 46	HR	HR	HR	LR	LR	LR	LR	HR	LR	LR	MR
Philippon et al 53	HR	HR	HR	LR	LR	HR	HR	LR	LR	LR	MR
Pizzolatti et al 47	HR	HR	HR	LR	LR	LR	HR	HR	LR	LR	MR
Register et al 49	HR	HR	HR	LR	LR	HR	HR	LR	LR	LR	MR
Schmitz et al 50	HR	HR	HR	LR	LR	LR	LR	LR	LR	HR	MR
Silvis et al 48	HR	HR	HR	HR	LR	HR	HR	LR	LR	LR	HR
Teichtahl et al 68	HR	HR	HR	LR	LR	LR	LR	LR	HR	LR	MR
Tresch et al 66	HR	HR	HR	LR	LR	LR	HR	HR	LR	LR	MR
Yuan et al 54	HR	HR	HR	HR	LR	HR	HR	HR	LR	HR	HR

Risk of bias items.
1. Was the study’s target population a close representation of the national population in relation to relevant variables, for example, age, sex, occupation?
2. Was the sample frame a true or close representation of the target population?
3. Was some form of random selection used to select the sample, or, was a census taken?
4. Was the likelihood of non-response bias minimal?
5. Were data collected directly from the subjects (as opposed to a proxy)?
6. Was an acceptable case definition used in the study?
7. Was the study instrument that measured the parameter of interest (eg, prevalence of low back pain) shown to have reliability and validity (if necessary)?
8. Was the same mode of data collection used for all subjects?
9. Was the length of the shortest prevalence period for the parameter of interest appropriate?
10. Were the numerator(s) and denominator(s) for the parameter of interest appropriate?
HR, high risk of bias; LR, low risk of bias; MR, moderate risk of bias.