[R] Help with factor levels and reference level

Nwinters nicholas.winters at mail.mcgill.ca
Fri Jun 6 20:16:11 CEST 2014

I have a variable coded in Stata as follows:
*gen sat_pm25cat_=.
replace sat_pm25cat_= 1 if (sat_pm25>=4 & sat_pm25<=7.1 & sat_pm25!=.)
replace sat_pm25cat_= 2 if (sat_pm25>=7.1 & sat_pm25<=10)
replace sat_pm25cat_= 3 if (sat_pm25>=10.1 & sat_pm25<=11.3)
replace sat_pm25cat_= 4 if (sat_pm25>=11.4 & sat_pm25<=12.1)
replace sat_pm25cat_= 5 if (sat_pm25>=12.2 & sat_pm25<=17.1)

gen satpm25catR= "A" if sat_pm25cat_==1
replace satpm25catR= "B" if sat_pm25cat_==2
replace satpm25catR= "C" if sat_pm25cat_==3
replace satpm25catR= "D" if sat_pm25cat_==4
replace satpm25catR= "E" if sat_pm25cat_==5

my model for R is:
*glm.PM25linB <-glm(leuk ~ satpm25catR + sex + ageR, data=leuk,
family=binomial, epsilon=1e-15, maxit=1000)*

In the summary, satpm25catR is being reported as all levels:


*What I want is to make "A" the reference level, how do I do this??*
Thank you

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