Table 2 Methodological quality assessment of included studies based on the Newcastle–Ottawa Scale

Link et al. (2008)

Case–control

*

*

*

*

**

*

*

********

Carr et al. (2013)

Case–control

*

*

*

*

*

*

*

*******

Marciante et al. (2011)

Case–control

*

*

*

*

*

*****

Brunham et al. (2012)

Case–control

*

*

*

*

**

*

*

*

*********

Voora et al. (2009)

Cohort

*

*

*

*

*

*

*

*******

Danik et al. (2013)

Cohort

*

*

*

*

*

*

*

*******

Donnelly et al. (2011)

Cohort

*

*

*

*

*

*

*

*******

de Keyser et al. (2014)

Cohort

*

*

*

*

**

*

*

********

de Keyser et al. (2014)

Cohort

*

*

*

*

**

*

*

********

de Keyser et al. (2014)

Cohort

*

*

*

*

**

*

*

********

de Keyser et al. (2014)

Cohort

*

*

*

*

**

*

*

********

Santos et al. (2012)

Cohort

*

*

*

*

*

*

*

*

********

Linde et al. (2010)

Cohort

*

*

*

*

*

*****