The quality assessment of included studies.

*1 indicates case definition and diagnostic appropriate; 2, consecutive patients or case having a good representation; 3, community controls; 4, control with no the history of study disease; 5A, according to the most important factor to select and analyze control; 5B, according to the second important factor to select and analyze control; 6, ascertainment of exposure by blinded interview or record; 7, same method of ascertainment used for cases and controls; and 8, non-response rate the same for cases and controls.