Dealing with confounding in observational studies.

it is a cause of the outcome, and it is not in the causal pathway between the main exposure and the outcome of interest. In B, obesity is a confounder in the relation between asthma and lung function since obesity may worsen asthma and may cause a reduction in lung function. Adjusting for obesity is advised in this scenario. In C, the model represents a mediation effect —obstructive sleep apnea may lead to cardiovascular disease (direct effect), but obstructive sleep apnea may also lead to high blood pressure, which causes cardiovascular disease (indirect effect). In this case, adjusting for high blood pressure is not appropriate