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Understanding Causality in Epidemiological Studies

Explore methods to interpret epidemiological studies, assess associations, and weigh evidence for causality, chance, bias, and confounding in Module 4. Supported by National Institute on Drug Abuse grant.

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Understanding Causality in Epidemiological Studies

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  1. Module 4 Overview Context Content Area: Interpretation of Epidemiological Evidence Essential Question (Generic): Is the association causal? Essential Question (Drug Abuse Specific): Is an association with drug abuse causal? Enduring Epidemiological Understanding: Causation is only one explanation for finding an association between an exposure and a disease. Because observational studies are complicated by factors not controlled by the observer, other explanations must also be considered. Synopsis: In Module 4, students explore the rationale and methods of interpreting epidemiological studies. Students develop skills to assess possible explanations for an association found in a study, with consideration of explanations of causality, chance, confounding, reversed time order, and bias. Module 4 concludes with consideration of methods for weighing the overall evidence for an association. Lessons: Lesson 4-1: Introduction to Interpreting Associations Lesson 4-2: Causality Lesson 4-3: Chance Lesson 4-4: Bias Lesson 4-5: Confounding Lesson 4-6: Reverse Time Order Lesson 4-7: Weighing the Evidence

  2. Module 4 - Interpretation of Epidemiological Evidence • Lesson 4-1 Introduction to Interpreting Associations • Content • Review of definition of association • Distinction between association and causation • Five possible explanations for an association • Big Ideas • Association does not necessarily mean causation • When an association is found in a study, several possible explanations must be considered, including causality, chance, bias, confounding, and reverse time order This project is supported by a Science Education Drug Abuse Partnership Award, Grant Number 1R24DA016357-01, from the National Institute on Drug Abuse, National Institutes of Health.

  3. Where are we? Essential Questions Enduring Understandings

  4. DZ E % Hypothesis or DZ % or Healthy People Healthy People DZ E - ? DZ Risk Relative Risk Total Exposure Outcome a b c d Turned Up Together Concept Map So Far . . . The Science of Public Health: Epidemiology

  5. DZ E % or DZ % or Healthy People Healthy People DZ E - ? DZ Risk Relative Risk Total Exposure Outcome a b c d Turned Up Together Concept Map . . Where We Are Going . . . Person, Place, Time Surveillance Hypothesis Testing Hypotheses Interpretation?

  6. Review - Definition of an Association Tied Related Associated Linked Optional - Use if needed for a concept connection What do we mean when we say that there is anassociationbetween two things? Things that are associatedare linked in some way that makes themturn up together.

  7. Review - Showing that Things Turn Up Together Outcome Optional - Use if needed for a concept connection No Outcome Outcome a b Exposure c d Exposure No Exposure

  8. Study Interpretation Interpret To give the meaning of, explain, or make clear.

  9. Review - Things That Turn Up Together Suicide Higher in Areas with Guns Smoking Linked to Youth Eating Disorders Family Meals Are Good for Mental Health Study Links Iron Deficiency to Math Scores Study Concludes: Movies Influence Youth Smoking Lack of High School Diploma Tied to US Death Rate Study Links Spanking to Aggression Depressed Teens More Likely to Smoke Snacks Key to Kids’ TV- Linked Obesity: China Study Breakfast Each Day May Keep Colds Away Pollution Linked with Birth Defects in US Study Kids Who Watch R-Rated Movies More Likely to Drink, Smoke

  10. IS ASSOCIATED WITH IN Is the Association Causal?

  11. Possible Reasons Why Things Turn Up Together Suicide Higher in Areas with Guns Family Meals Are Good for Mental Health 1. Cause Study Links Iron Deficiency to Math Scores Study Concludes: Movies Influence Youth Smoking 2. Chance 3. Bias Lack of High School Diploma Tied to US Death Rate Study Links Spanking to Aggression Confounding 4. Depressed Teens More Likely to Smoke Snacks Key to Kids’ TV- Linked Obesity: China Study 5. Reverse Time Order Pollution Linked with Birth Defects in US Study Kids Who Watch R-Rated Movies More Likely to Drink, Smoke

  12. Exercise in Interpreting an Association Association Found Between Coffee and Pancreatic Cancer

  13. Possible Explanations for Finding an Association 1. Cause 2. 3. 4. 5.

  14. Explanation 1 - Causal Cause Anything that produces an effect

  15. Explanation 1 - Causal Risk Factor An exposure that increases the likelihood of a specific outcome.

  16. Explanation 1 - Causal Some high school students’ answers that indicate they think that “association always means causation”“Association means that the two things are related, or that one leads to another or one is the cause / effect of the other.”“When you say that two things are associated with each other you mean that there is a direct relation between the two things - that one thing can cause another thing to occur.”“To be ‘associated with’ as in the context of coffee and pancreatic cancer means that coffee is a cause or at least part of the etiology which results in pancreatic cancer.“ “An addition or lack of one thing will cause an appreciable change in the other.”“When it is said, something associated with another, it means that they share a common bond, usually one of cause and effect.”

  17. Possible Explanations for Finding an Association 1. Cause 2. Chance 3. 4. 5.

  18. To occur accidentally To occur without design A coincidence Explanation 2 - Chance Chance

  19. Possible Explanations for Finding an Association 1. Cause 2. Chance 3. Bias 4. 5.

  20. Explanation 5 - Study Bias Bias Any systematic error in the design, conduct, or analysis of a study that results in a mistaken estimate of an exposure’s effect on the risk of the outcome. Leon Gordis, Epidemiology, 3rd Edition, Elsevier Saunders, 2004.

  21. Possible Explanations for Finding an Association 1. Cause 2. Chance 3. Bias Confounding 4. 5.

  22. Explanation 3 - Confounding Confounding A situation in which an association between a given exposure and an outcome is observed as a result of the influence of a third unobserved factor, called a confounder.

  23. Explanation 3 - Confounding Confounding A situation in which an association between a given exposure (match carrying) and an outcome (lung cancer) is observed as a result of the influence of a third unobserved factor, called a confounder (smoking) Obviously we should have measured smoking

  24. Association Cause X Cause Lung Cancer Match-Carrying Diagram of Confounding Confounder Not Observed Smoking Observed

  25. Possible Explanations for Finding an Association 1. Cause 2. Chance 3. Bias Confounding 4. 5. Reverse Time Order

  26. Egg Chicken Explanation 4 - Reverse Time Order ? Hypothesized Exposure Outcome

  27. Explanation 4 - Reverse Time Order Hypothesized Exposure Outcome Violent Behavior Playing Violent Video Games

  28. Possible Explanations for Finding an Association To reiterate . . . 1. Cause 2. Chance 3. Bias Confounding 4. 5. Reverse Time Order The Science of Public Health: Epidemiology

  29. Review - Definition and Purpose of Epidemiology ... the study of the distribution and determinants of health-related states or events in specified populations and the application of this study to the controlof health problems. (Gordis, 2004) How do the five possible explanations relate to the idea that epidemiology studies are done for purposes of eventually controlling health problems?

  30. X … and you avoided or eliminated the hypothesized cause, what would happen to the outcome? Possible Explanations for Finding an Association If an association was causal, …. causal, …. ? Exposure Outcome X

  31. X … and you avoided or eliminated the hypothesized cause, what would happen to the outcome? Possible Explanations for Finding an Association If an association was found due to chance, …. found due to chance, …. ? Exposure Outcome

  32. X … and you avoided or eliminated the hypothesized cause, what would happen to the outcome? Possible Explanations for Finding an Association If an association was found due to bias, …. found due to bias, …. ? Exposure Outcome

  33. found due to confounding, …. Unobserved Exposure X … and you avoided or eliminated the hypothesized cause, what would happen to the outcome? Possible Explanations for Finding an Association If the association was found due to confounding, …. ? Exposure Outcome

  34. found due to reverse time order, …. X … and you avoided or eliminated the hypothesized cause, what would happen to the outcome? Possible Explanations for Finding an Association If an association was found due to reversed time-order, …. ? Exposure Outcome

  35. Big Ideas • So with one explanation - causality - removing the exposure away would lead to prevention • But for the other four explanations - chance, confounding, reverse time order and bias - removing the exposure won’t change anything • So we need to interpret studies correctly to avoid wasting time and resources on preventing exposures that will not lead to prevention of disease

  36. Exercise in Interpreting an Association Optional Association Found Between Coffee and Pancreatic Cancer

  37. Always Remember Association is not necessarily causation. Association is not necessarily causation. Association is not necessarily causation. Association is not necessarily causation. Association is not necessarily causation. Association is not necessarily causation. Association is not necessarily causation. Association is not necessarily causation.

  38. Don’t Forget Association is not necessarily causation. Association is not necessarily causation. Association is not necessarily causation. Association is not necessarily causation. Association is not necessarily causation. Association is not necessarily causation. Association is not necessarily causation. Association is not necessarily causation.

  39. Re-Cap • Big Ideas in this Lesson (4-1) • Association does not necessarily mean causation • When an association is found in a study, several possible explanations must be considered, including causality, chance, bias, confounding, and reverse time order This project is supported by a Science Education Drug Abuse Partnership Award, Grant Number 1R24DA016357-01, from the National Institute on Drug Abuse, National Institutes of Health.

  40. Next Lesson Causality SURGEON GENERAL’S WARNING:Smoking Causes Lung Cancer, Heart Disease, Emphysema, and May Complicate Pregnancy

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