Example 9 and Table 4.3 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/(688 + 650) ) and proportion of nonsmokers who had lung cancer (21/(21 + 59)) to estimate corresponding proportions of smokers and nonsmokers who have lung cancer in the overall population.