A Comorbid Mental Disorder Paradox: Using Causal Diagrams To Understand Associations Between Posttraumatic Stress Disorder And Suicide

Although Some Studies Document That Posttraumatic Stress Disorder (Ptsd) Increases Suicide Risk, Other Studies Have Produced The Paradoxical Finding That Ptsd Decreases Suicide Risk. We Sought To Understand Methodologic Biases That May Explain These Paradoxical Findings Through The Use Of Directed Acy-Clic Graphs (Dags). Method: Dags Are Causal Diagrams That Visually Encode A Researcher’S Assumptions About Data Generating Mechanisms And Assumed Causal Relations Among Variables. Dags Can Connect Theo-Ries To Data And Guide Statistical Choices Made In Study Design And Analysis. In This Article, We Describe Dags And Explain How They Can Be Used To Identify Biases That May Arise From Inappropriate Analytic Deci-Sions And Data Limitations. Results: We Define A Particular Form Of Bias, Collider Bias, That Is A Likely Explana-Tion For Why Studies Have Found A Supposedly Protective Association Of Ptsd With Suicide. This Protective Association Is Interpreted By Some Researchers As Evidence That Ptsd Reduces The Risk Of Suicide. Collider Bias May Occur Through Inappropriate Adjustment For A Psychiatric Comorbidity, Such As Adjustment For Varia-Bles That Are Affected By Ptsd And Share Common Causes With Suicide. Conclusions: We Recommend That Researchers Collect Longitudinal Measurements Of Psychiatric Comorbidities, Which Would Help Establish The Temporal Ordering Of Variables And Avoid The Biases Discussed In This Article.