Compare smokers with nonsmokers Example 8 and Table 4.2 described a case-control study on smoking and lung cancer. Explain carefully why it is not sensible to use the study’s proportion of smokers who had lung cancer

(that is, 688> 1688 + 6502) and proportion of nonsmokers who had lung cancer 121> 121 + 5922 to estimate corresponding proportions of smokers and nonsmokers who have lung cancer in the overall population.