More Groups
Fewer Groups
More People
Fewer People
Yu, G. P.; Ostroff, J. S.; Zhang, Z. F.; Schantz, S. P. American Journal of Epidemiology (1996)
Begg, C. B.; Zhang, Z. F.; Sun, M.; Herr, H. W.; Schantz, S. P. American Journal of Epidemiology (1995)