1. There is growing interest in whether inflammation is important in the pathogenesis of coronary artery disease (CAD) and whether the presence of certain inflammatory diseases outside of the heart can influence the risk of development of CAD. Specifically, there is interest in the role of periodontal disease. To address this, a cohort study was performed to evaluate the independent association between periodontal disease (inflammation of the gums and other soft tissue in the mouth) and the occurrence of CAD. The unadjusted (crude) analysis found that those persons with periodontal disease at baseline have a higher rate of CAD than persons without periodontal disease. Assessment of plasma level of C-reactive protein (CRP) was also performed at baseline. CRP level is known to be elevated in many inflammatory conditions and has also been associated with the development of coronary artery disease. In this cohort study, after adjustment for CRP level, the association between periodontal disease and coronary artery disease was no longer present. 

Using causal diagrams (DAGs) as described in class, diagram two possible scenarios that could explain why adjustment for CRP resulted in you no longer seeing an effect for periodontal disease.