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Conducting Logistic Regression in R
Below is computer code written in the R programming language that conducts logistic regression analysis. Just copy and paste it into R and watch it rip. The data set for this R program can be found HERE.
# First we get our data.
mydata < read.table("panel80.txt")
# attach(mydata) # In case you want to work with the variable names directly
names(mydata) # This shows us all the variable names.
# options(scipen=20) # suppress "scientific" notation
options(scipen=NULL) # Brings things back to normal
# Now we want to make a binary response variable that has a vote for Carter=0 and a vote for Reagan=1.
mysubsetdata1 < subset(mydata, VOTE == 1  VOTE==2) # This keeps only those respondents who actually voted for Carter or Reagan.
mysubsetdata2<subset(mysubsetdata1, select=c(VOTE, REAFEEL3, CARFEEL3, INC, AGE, PARTYID)) #This keeps only the variables that we are using.
#mysubsetdata2
# In VOTE, a vote for Reagan=1 and a vote for Carter=2. We change that in the loop below when we create the new variable binaryvote.
binaryvote < 0
# This initializes the binaryvote variable.
for (i in 1:nrow(mysubsetdata2)) {
if (mysubsetdata2$VOTE[i]==2) binaryvote[i]=0 else binaryvote[i]=1
}
# Here is another way to do the same thing in one line.
binaryvote2 < ifelse((mysubsetdata2$VOTE == 1), 1, 0)
mysubsetdata3<cbind(mysubsetdata2, binaryvote, binaryvote2)
mysubsetdata3
# Now we do the logistic regression.
logitvote.model < glm(binaryvote ~ INC + AGE + PARTYID, family=binomial, data=mysubsetdata3)
summary(logitvote.model)
# Now we get the individual risk factors (or odds ratios).
round(exp(cbind(Estimate=coef(logitvote.model), confint(logitvote.model))), 2) # The 2 at the end is the number of decimals we want.
