"Putting It Together: Passive Smoke? The following abstract appears in The New England Journal of Medicine:BACKGROUNDThe 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.METHODSIn 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.RESULTSHousehold 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.CONCLUSIONSThe 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.


What makes this study a case-control study? Why is this a retrospective study?"

Verified step by step guidance

1. Identify the defining characteristic of a case-control study: it involves selecting participants based on their outcome status, meaning one group has the condition (cases) and the other does not (controls).
2. Note that in this study, the researchers selected 191 patients who have lung cancer (cases) and an equal number of persons without lung cancer (controls), which fits the case-control design.
3. Understand that a retrospective study looks backward in time to examine exposures or risk factors that might have contributed to the outcome.
4. Recognize that this study collected lifetime residential histories and past exposure to environmental tobacco smoke, meaning the researchers gathered data about participants' past exposures after the lung cancer diagnosis.
5. Conclude that because the study starts with known outcomes (lung cancer or no lung cancer) and looks back to assess exposure history, it is both a case-control and a retrospective study.

Key Concepts

Case-Control Study Design

A case-control study compares individuals with a specific condition (cases) to those without it (controls) to identify factors associated with the condition. It is observational and often used to study rare diseases or outcomes. In this study, lung cancer patients (cases) are compared to non-cancer individuals (controls) to assess exposure to passive smoking.

Retrospective Study

A retrospective study looks backward in time, collecting past data on exposures or risk factors after the outcome has occurred. Researchers rely on existing records or participant recall. This study is retrospective because it gathers historical exposure information (smoker-years) after lung cancer diagnosis.

Exposure Measurement and Recall Bias

Exposure measurement quantifies how much participants were exposed to a risk factor, here using 'smoker-years' to capture intensity and duration. Recall bias occurs when participants inaccurately remember past exposures, potentially skewing results. The study acknowledges this as a limitation due to reliance on participants’ memory of household smoking.