The following abstract appears in The New England Journal of Medicine:
The relation between passive smoking and lung cancer is of great public health importance.
Some previous studies have suggested that exposure to environmental tobacco smoke in the household can cause lung cancer, but others have found no effect. Smoking by the spouse has been the most commonly used measure of this exposure.
METHODS. In order to determine whether lung cancer is associated with exposure to tobacco smoke within the household, we conducted a case-control study of 191 patients with lung cancer who had never smoked and an equal number of persons without lung cancer who had never smoked. Lifetime residential histories including information on exposure to environmental tobacco smoke were compiled and analyzed. Exposure was measured in terms of “smoker-years,” determined by multiplying the number of years in each residence by the number of smokers in the household.
RESULTS. Household exposure to 25 or more smoker-years during childhood and adolescence doubled the risk of lung cancer. Approximately 15 percent of the control subjects who had never smoked reported this level of exposure. Household exposure of less than 25 smoker-years during childhood and adolescence did not increase the risk of lung cancer. Exposure to a spouse’s smoking, which constituted less than one third of total household exposure on average, was not associated with an increase in risk.
CONCLUSIONS. The possibility of recall bias and other methodologic problems may influence the results of case-control studies of environmental tobacco smoke. Nonetheless, our findings regarding exposure during early life suggest that approximately 17 percent of lung cancers among nonsmokers can be attributed to high levels of exposure to cigarette smoke during childhood and adolescence.
(a) What is the research objective?
(b) What makes this study a case-control study? Why is this a retrospective study?
(c) What is the response variable in the study? Is itqualitative or quantitative?
(d) What is the explanatory variable in the study? Is it qualitative or quantitative?
(e) Can you identify any lurking variables that may have affected this study?
(f ) What is the conclusion of the study? Can we conclude that exposure to smoke in the household causes lung cancer?
(g) Would it be possible to design an experiment to answer the research question in part Explain.

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