Table 2 Methodological quality of included studies

Adequate definition of cases

*

*

*

*

*

*

Representativeness of cases

–

–

–

–

*

–

Selection of control subjects

*

–

–

–

–

–

Definition of control subjects

*

*

*

*

*

*

Control for important factor or additional factor

*

*

**

–

**

*

Exposure assessment

*

*

*

*

*

*

Same method of ascertainment for all subjects

*

*

*

*

*

*

Non-response rate

*

*

*

*

*

*