The data in Table 14.6 concerning the relationship between smoking and lung cancer death are presented in a course of The Open University, Statistics in Society, Unit C4, The Open University Press, Milton Keynes, England, 1983. The original source of the data is Occupational Mortality: The Registrar General’s Decennial Supplement for England and Wales, 1970–1972, Her Majesty’s Stationery Office, London, 1978. In the table, a smoking index greater (less) than 100 indicates that men in the occupational group smoke more (less) than average when compared to all men of the same age. Similarly, a lung cancer death index greater (less) than 100 indicates that men in the occupational group have a greater (less) than average lung cancer death rate when compared to all men of the same age. In Figure 14.39 we present a portion of a MINITAB output of a simple linear regression analysis relating the lung cancer death index to the smoking index. In Figure 14.40 we present a plot of the lung cancer death index versus the smoking index.

a. Although the data do not prove that smoking increases your chance of getting lung cancer, can you think of a third factor that would cause the two indexes to move together?
b. Does the slope of the hypothetical line relating the two indexes when the smoking index is less than 100 seem to equal the slope of the hypothetical line relating the two indexes when the smoking index is greater than 100? If you wish, use simple linear regression to make a more precise determination. What practical conclusion might you make?

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TABLE 14.6 The Smoking and Lung Cancer Death Data OS Smoking Smoking Index 77 137 117 94 116 102 111 93 88 102 Occupational Group Farmers, foresters, and fisherman Miners and quarrymen Gas, coke, and chemical makers Glass and ceramics makers Furnace, forge, foundry, and rolling mill workers Electrical and electronics workers Engineering and allied trades Woodworkers Leather workers Textile workers Clothing workers Food, drink, and tobacco workers Paper and printing workers Makers of other products Construction workers Painters and decorators Drivers of stationary engines, cranes, etc. Laborers not included elsewhere 91 104 107 112 113 110 125 133 Transport and communications workers 115 Warehousemen, storekeepers, packers, and bottlers 105 87 91 100 76 66 Clerical workers Sales workers Service, sport, and recreation workers Administrators and managers Professionals, technical workers, and artists Lung Cancer Death Index 84 116 123 128 155 101 118 113 104 88 104 129 86 96 144 139 113 146 128 115 79 85 120 60 51