Table 2 Quality appraisal of included studies

Dirmaier et al. [43]

1.

Were the two groups similar and recruited from the same population?

X

2.

Were the exposures measured similarly to assign people to both exposed and unexposed groups?

X

3.

Was the exposure measured in a valid and reliable way?

X

4.

Were confounding factors identified?

X

5.

Were strategies to deal with confounding factors stated?

X

6.

Were the groups/participants free of the outcome at the start of the study (or at the moment of exposure)?

X

7.

Were the outcomes measured in a valid and reliable way?

X

8.

Was the follow-up time reported and sufficient to be long enough for outcomes to occur?

X

9.

Was follow-up complete, and if not, were the reasons to loss to follow-up described and explored?

X

10.

Were strategies to address incomplete follow-up utilized?

X

11.

Was appropriate statistical analysis used?

X

Shin et al. [44]

1.

Were the criteria for inclusion in the sample clearly defined?

X

2.

Were the study subjects and the setting described in detail?

X

3.

Was the exposure measured in a valid and reliable way?

X

4.

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

X

5.

Were confounding factors identified?

X

6.

Were strategies to deal with confounding factors stated?

X

7.

Were the outcomes measured in a valid and reliable way?

X

8.

Was appropriate statistical analysis used?

X