The pheno data set contains phenotype information for 2457 subjects from the Finland-United States Investigation of NIDDM Genetics (FUSION) study of type 2 diabetes [SMS+04]. Among the physical measurements recorded is the height (in cm) of the subjects.
a) Make a normal-quantile plot of the heights of all subjects in this data set. Do the heights appear to be normally distributed?
b) Now make conditional normal-quantile plots, conditioned on sex. Do the heights of the men and women in this study appear to be approximately normally distributed? If not, how do the distributions differ from a normal distribution?