Directed Acyclic Graphs, Hazard Ratios, Confounding
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Directed Acyclic Graphs (DAGs)
To complete this assignment, please review the article by Shrier and Platt (2008), located in the Learning Resources. You may use any drawing tools available to you to create the DAGs requested below, although it does not need to be sophisticated software; for example, Microsoft Word's Insert Shapes and Text Box features are sufficient tools to create these diagrams.
For each of the following epidemiological scenarios, draw a DAG that represents the relationships between the variables:
1) A researcher is studying the association between alcohol consumption (A) and the incidence of lung cancer (C). Smoking (S) is related to both variables.
2) A researcher is studying the association between automobile exhaust (E) and the prevalence of asthma in children (A). Other air pollutants (P) may also affect asthma prevalence. The presence of wind (W) affects the concentrations of both (E) and (P).
3) A researcher is studying the association between experiencing childhood abuse (A) and the occurrence of depression (D) as an adult. She has reason to believe that alcohol consumption (C) may mediate the relationship between (A) and (D).
Assessing Confounding in Multivariate Regression
A researcher studied women with breast cancer to better understand the association between self-rated health and breast cancer mortality (Prehn, 1996). By using survival analysis, the following results were obtained from three different models:
4) State in words the meaning of the hazard ratios for self-rated health in model 1.
5) State in words the meaning of the hazard ratios for self-rated health in model 3. Discuss whether or not breast cancer stage and daily task limitations were confounders of the self-rated health/mortality association. Justify your response and state your overall conclusions based on the analyses.
Prehn, A. W. (1996). Self-rated health in middle-aged and elderly women with breast cancer (Doctoral dissertation). Retrieved from Dissertation Abstracts International.
Draw three directed acyclic graphs (DAGs) representing relationships between variables in studies. Interpret hazard ratios and determine whether variables are confounding or not.