Table 5.

Risk of Bias, Case–Control Studies

	1	2	3	4	5	6	7	8	9
Atallah et al2	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
He et al6	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Roy et al18	Yes	Yes	Yes	Yes	Yes	Yes	Cannot tell	Yes	Yes

Notes:

1. Did the study address a clearly focused issue?
2. Did the authors use an appropriate method to answer their question?
3. Were the cases recruited in an acceptable way?
4. Were the controls selected in an acceptable way?
5. Was the exposure accurately measured to minimize bias?
6. Have the authors taken account of the potential confounding factors in the design and/or in their analysis?
7. Do you believe the results?
8. Can the results be applied to the local population?
9. Do the results of this study fit with other available evidence?