Hein Stigum http://folk.uio.no/heins/ courses E8 DAGs intro 2h, Answers Hein Stigum http://folk.uio.no/heins/ courses 17. apr. H.S.

Exercise: Physical activity and Coronary Heart Disease (CHD) We want the total effect of Physical Activity on CHD. What would we adjust for? Unconditional   Path Type Status 1 E®D Causal Open 2 E¬C1®D Non-causal 3 E¬C2®D Bias Noncausal open=biasing path Conditioning on C1 and C2   Path Type Status 1 E®D Causal Open 2 E¬[C1]®D Non-causal Closed 3 E¬[C2]®D No bias Apr-17 Apr-17 Apr-17 H.S. H.S. 2 2

Tea and depression Total effect: adjust for O Direct effect: adjust for C (and O) Caffeine is both intermediate and part of a confounder path.   Path Type Status 1 E→D Causal Open 2 E→C→D 3 E←O→C→D Non-causal Tea and depression: Finnish study Caffeine reduces depression: Nurses Health Study direct total indirect Apr-17 H.S.

Statin and CHD We want the total effect of statin on CHD. What would you adjust for? Can we estimate the direct effect of statin on CHD (not mediated through cholesterol)? No adjustments gives the total effect Adjusting for C will close path 2 but will open path 3 and give bias! C is a collider on path 3 Apr-17 H.S.

Survival bias Conclusion: Have survival bias risk Paths: ED Causal Open E[S]RD Non-causal Open E early exposure D later disease E and R are unrelated causes for disease Conclusion: Have survival bias Must adjust for R to remove the bias 17. apr. H.S.

Exercise: causal pies Sufficient causes for Hospital: Selection bias: Causal pies for hospital Selection bias: Sufficient causes for Hospital: 1) or 2) and 3) both Selection bias: Negative bias Positive bias ? Apr-17 H.S.

Exercise: Collider stratification Hospital risk: Selection bias Collider stratification bias Apr-17 H.S.