我有数据如下：
(EDU_IRON<-data.frame(
EDUCAT=c("UNDER 12YRS","UNDER 12YRS","12YRS OR MORE","12YRS OR MORE"),
IRON=c("D","A","D","A"),
N=c(4,26,4,66)
))

我想跑一个无截距的模型
glm(IRON~0+EDUCAT,data=EDU_IRON,family=binomial,weights=N)
但是出来的系数有两个，EDUCAT12YRS OR MORE ，EDUCATUNDER 12YRS，我想把EDUCATUNDER 12YRS作为参考组，即他的系数为0，这个怎样实现？