Table 1 Study designs and quality scoring according to the Newcastle Ottawa scale of non-randomized studies in meta-analysis and subsequent classification according to AHRQ standards

Fedeli et al.

Case control

**

*

**

Moderate

Das-Munshi et al.

Cohort

***

*

***

High

Carey et al.

Cohort

***

*

***

High

Shiels et al.

Cohort

**

*

**

Moderate

Axenhus et al.

Cohort

**

*

**

Moderate

Reif et al.

Cohort

*

–

**

Low

Raknes et al.

Cohort

**

–

**

Low

Lee et al.

Cohort

**

*

**

Moderate

Strongman et al.

Cohort

***

*

***

High

Gilstrap et al.

Cohort

**

*

***

Moderate

Grande et al.

Cohort

**

–

**

Low