[55 points] (public health) in 1972 a one-in-six random survey of the electoral roll | largely concerned with studying heart disease and smoking | was carried out in whickham, a mixed urban and rural district near newcastle upon tyne in england. twenty years later a follow-up study was conducted, with the results published in the journal clinical endocrinology in 1995. the dataset summarized below in this problem pertains to the subsample of 1,314 women in the study who were classi ed in the original survey either as current smokers or as never having smoked. there were relatively few women (162) who had smoked but stopped, and only 18 whose smoking habits were not recorded; these women are not included in the data here. the 20-year survival status was determined for all the women in the original survey. the outcome variable y of interest here was mortality, recorded as dead or alive in 1992; the re- searchers regarded x, smoking behavior in 1972 (current smoker or never smoked), as the supposedly causal factor (scf), and they also measured the variable z, age (18{64 or 65+) in 1972. several de nitions and conclusions from the eld of experimental design are relevant here: