Table 3.

A quality scoring system for case-control studies

First author	Was exposure assessment the same for cases and controls?	Were exposure assessors blind to case-control status?	Were cases and controls from the same population?	Were the number and reasons for study withdrawals reported?
	Yes (2), Partial (1), No (0)	Yes (2), Partial (1), No (0)	Yes (2), Partial (1), No (0)	Yes (2), Partial (1), No (0)
Pouw 2000	2	0	2	1
Bourbeau 2003	2	0	2	0
Garcia-Aymerich 2001	2	0	2	2