DAG #1 Exposure: Lifestyle choices Disease: Parkinson’s disease DAG #2 Primary Exposure: Lifestyle choices Disease: Parkinson’s disease Other risk factor: Smoking FINAL DAG Primary Exposure: Lifestyle choices Disease: Parkinson’s disease Other risk factor: Smoking Confounder: Age + Diet Interpretation: The above DAG captures three known key casual influences of Parkinson’s disease: Lifestyle choices, Diet and Age. It also demonstrates the influence of Age on the primary exposure; lifestyle choices. The DAG also illustrates Occupation as a mediator variable. Smoking is associated with exposure of lifestyle choice and can be used as a proxy to determine the effect of the exposure on the outcome (PD). Age is a confounder in this DAG and is a common factor in lifestyle choices and Parkinson’s disease. Confounding is present when we want to assess the casual relationship between the exposure (lifestyle choice) and the outcome (PD). For example, having a poor diet increases the likelihood of developing PD. Having a poor diet is also a lifestyle choice, which in turn can lead to developing Parkinson’s disease. This DAG does not include a “back-door” path that need to be addressed. For observational studies, controlling for confounders is vital, considering subjects are not randomly assigned to different groups. If we want to achieve an unbiased assessment of the exposure-outcome relationship, identifying confounders, collecting relevant information on them, design studies appropriately, taking confounders into account and adjusting for confounding in data analysis. Depending on the confounders’ true relationship to the exposure and outcome, adjustments for confounders can sometimes introduce a new bias. In order to reduce this from happening, researchers should carefully consider which confounders to include their model rather than including all potential confounders related to the exposure of outcome.
