Brief Look at Association vs causation
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A very brief summary of causation vs. association, causal pathways, the Bradford Hill Criteria, and Pyramid of Clinical Evidence.
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Brief Look at Association vs causation
- 1. Association vs. Causation Patrick B. Barlow PhD Candidate in Evaluation, Statistics, & Measurement The University of Tennessee This and many other lecture materials are available at www.slideshare.net/pbbarlow1
- 2. In this Presentation… Section I: Association vs. Causation, what does it look like? Conceptually speaking Casual Pathways Section II: Methods for judging strength of causal relationship Bradford Hill Criteria Pyramid of Clinical Evidence
- 3. Some Terms Association Causation Causal Pathway Interaction / Effect Modification Confounding / Mediation
- 4. Association vs. Causation Conceptually Speaking Association Correlation Regression Odds / Relative Risk Causation Influence Effect Confounding Explanation Dependence Intervention Likelihood Randomization Conditional Attribution Adapted From: Joffe et al. Emerging Themes in Epidemiology 2012
- 5. Association vs. Causation Conceptually Speaking Association Two observed variables that are jointly distributed Can be strong, weak, positive, or negative. Causation “A causal relationship is one that has a mechanism that by its operation makes a difference” (Joffe et al., 2012). For example:
- 6. Causal Pathways When in doubt, draw it out! Causal Pathways Visual depictions of the proposed links between a given exposure(s) and the outcome of interest. They help researchers understand the mechanisms at work in a complex disease process. Exposure ? Outcome
- 7. Types of Causal Pathways Simple (Direct) Confounding (Mediation) Effect Modification (Moderation) Exposure Exposure Exposure ? ? Outcome Confounder ? Outcome Effect Moderator ? Outcome
- 8. Types of Causal Pathways Simple (Direct) Confounding (Mediation) Effect Modification (Moderation) Diet Diet Diet ? ? CAD Smoking Hx ? CAD Activity Level ? CAD Examples adapted from CTSPedia.com
- 9. Methods for Judging Strength of Causal Relationship Bradford Hill Criteria Pyramid of Clinical Evidence
- 10. The Bradford Hill Criteria Provides researchers with seven criteria for assessing strength of evidence. Strength of association (i.e. effect size) Consistency (i.e. reliability) Specificity Temporal relationship Biological gradient Plausibility Coherence Experiment (reversibility) Analogy (consideration of alternate explanations)
- 11. The Bradford Hill Criteria a closer look… Strength of association (i.e. effect size) Is the magnitude of the association both statistically and clinically meaningful? Consistency (i.e. reliability) Can these results be reproduced? Do they coincide with existing research on the same phenomenon? Specificity Association is specific when the exposure is associated with only one disease Temporal relationship Does the exposure (cause) precede the outcome (effect)?
- 12. The Bradford Hill Criteria a closer look… Biological gradient Dose-response relationship can be established Biological Plausibility Is the association coherent with the current body of biologic knowledge? Coherence Is the association plausible given what we already know about the disease or disorder? Experimental evidence Has this association been shown in a randomized experimental trial? Analogy (consideration of alternate explanations) Have all other plausible alternative explanations been considered and ruled out? “The third variable issue”
- 13. Strength of Evidence & Study Design Which criteria are difficult to satisfy with… Case – Control studies? Cross – Sectional studies? Cohort – Studies?
- 14. Pyramid of Clinical Evidence Systematic Reviews & Meta-analyses Cross-Sectional Studies: Level “2.3” Evidence Summaries RCT Cohort Studies Level 1 Evidence Level 2 Evidence Case Control Studies Level 3 Evidence Case Series Case Reports Ideas, Editorials, Opinions Animal research In vitro (‘test tube’) research
- 15. So, when reading an article… Whenever digging into a new controversy or research area, it is helpful to use methods for judging the strength of the relationship being discussed. What type of study design are the using? (Pyramid of evidence) How strong is the evidence? (Bradford Hill Criteria) What is the clinical vs. statistical significance being presented?
Notas do Editor
- Cross-sectional Studies considered 2.3 by the OBGYN journal I looked at, but it is not technically a “Clinical” study.Double check to see if this is the same pyramid of evidence you see used in Epi.