"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.


Can you identify any lurking variables that may have affected this study?"

Verified step by step guidance

1. Understand the concept of lurking variables: these are variables that are not included in the study but may influence both the explanatory variable (exposure to tobacco smoke) and the response variable (lung cancer), potentially confounding the results.
2. Consider environmental factors that might correlate with both household smoking and lung cancer risk, such as air pollution, occupational exposures, or socioeconomic status, which were not explicitly controlled for in the study.
3. Think about genetic predispositions or family history of lung cancer that could affect lung cancer risk independently of passive smoking but might be unevenly distributed between cases and controls.
4. Reflect on lifestyle factors like diet, physical activity, or exposure to other carcinogens that might differ between the groups and influence lung cancer risk, yet were not accounted for in the analysis.
5. Recognize that recall bias itself can act as a lurking variable, where cases might remember or report exposure differently than controls, thus affecting the observed association.

Key Concepts

Lurking Variables

Lurking variables are hidden factors not accounted for in a study that can influence both the independent and dependent variables, potentially confounding the results. Identifying them is crucial because they may create a false association or mask a true relationship between variables, leading to incorrect conclusions.

Case-Control Study Design

A case-control study compares individuals with a condition (cases) to those without (controls) to identify factors associated with the condition. This retrospective design is efficient for rare diseases but is susceptible to biases like recall bias and confounding, which must be carefully considered when interpreting results.

Recall Bias

Recall bias occurs when participants in a study remember past exposures differently based on their disease status, often over-reporting or under-reporting certain factors. In case-control studies, this can distort the association between exposure and outcome, especially when relying on self-reported historical data.