1. Primary carcinoma of the gallbladder, analysis of 22 cases;Balaroutsos;Annals of Surgery,1971
2. Primary carcinoma of the gallbladder;Chao;Journal of Surgical Oncology,1991
3. Clarke M Oxman AD Cochrane Reviewers' Handbook 4.1.6 www.cochrane.dk/cochrane/handbook/handbook.htm
4. Epidemiology of gallbladder cancer: a synthesis of recent data;Diehl;Journal of National Cancer Institute,1980
5. Bias in meta-analysis detected by a simple graphical test;Egger;BMJ (Clinical Research Ed.),1997