Question

Epidemiologists conducted a case-control study of asthma and asked participants if they had ever worked in a factory. They stratified their analysis by smoking. Smoking is associated with asthma and working in a factory.

Odds ratio for smokers = 500x100/150x200 = 1.66

Odds ratio for non-smokers = 250x200/200x75= 3.33

Question- By looking at odd ratios, Do you think that there is confounding, effect modification, or neither in this study?

Answer 1

Among smokers odds of finding asthma is 1.66 the odds of finding someone with asthma among the controls. among nonsmokers, asthma exposure is only 3.33 higher the odds of finding with asthma exposure. There is an effect modification showing direct control measures it showing the effect of disease and risk factors. Asthma is high among nonsmokers when they working in a factory than smoking.
there is a confounding that has an association with exposure and outcome. the odds of finding someone who non smokes among the case is higher than the odds of finding someone with smoking exposure to asthma.
a confounder is a risk factor for the disease.it related the nonsmoking history and asthma, working in a factory is a confounder that is a risk factor of asthma, it can also a preventive factor for the disease.
confounding is a bias that provides potential confounding factors. effect modification differs from confounding, it shows the direct effect of the outcome. it has direct contact as a primary exposure of an outcome. it differs depending upon the third variable. exposure has a different impact in different situations. smoking is no exposure and not associated with the outcome, it helps to increase the finding. in this case, nonsmokers have a high risk of asthma than smoking. but at the same time working in the factory associated with more asthma risk.