可以用非参数检验的选项来做
http://wenku.baidu.com/link?url=LcGcmb-QHjevJ8U885FBIqvJTteBNGxt7QkQei_hxq4DCg6OlAhOA4PIk4hupxkHVflVTGyomPGmScvBPZV03tQPkB8mB_YnuqK_ExECKIa