Using the plasma retinol data in Chapter 1, remove the former smokers as well as the leverage points from the data set and use the R function logrsm to verify that as plasma beta-carotene increases, the likelihood that a participant is a smoker decreases. Also verify that when testing at the 0.05 level, you find an association based on a logistic regression model Hint: One way of pulling out the subset of values desired is as follows. First set yy=plasma[,3], xx=plasma[,13] and flag=(yy!=2).

Then yy[flag] and xx[flag] contain the data for never smoked and current smoker. To remove leverage points, set the argument xout=T.