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Introduction to Causality

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HSCI 330, Simon Fraser University

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Introduction to Causality

  1. 1. CAUSALIT Y INTRODUCTION TO HSCI 330
  2. 2. WARM-UP EXERCISE • With the person sitting next to you: 1. Select a “health related state or event” that interests you. 2. Create a mind map diagram linking as many relevant themes as you can to your selected state or event. • For example, if you choose Alzheimer’s disease you might include relationships between “beta amyloid plaques,” “neurofibrillary tangles,” “tau protein,” ,” “memory loss,” “exercise,” “saturated fats,” “care giver fatigue,” “pet therapy,” “cost of memory care,” etc. 3. After you have exhausted all themes and drawn the links between them, draw boundaries between the themes that cordon off themes into the following categories: “social,” “biological,” “cultural,” “structural,” and “epidemiological” issues. 4. Now identify pathways related to each of these categories for controlling the outbreak.
  3. 3. CAUSALITY • Aristotelian philosophy uses the word “cause” to mean “explanation” or to answer to the question “Why?”
  4. 4. EXPLANANDUM (explicandum) • An explanandum is a sentence describing a phenomenon that is to be explained
  5. 5. EXPLANANS (explicans) • Explanans are the sentences adduced as explanations of that phenomenon.
  6. 6. FOUR ARISTOTELIAN CAUSES • Matter – Material Cause • Form – Formal Cause • Agent – Efficient Cause • End – Final Cause
  7. 7. ARISTOTELIAN CAUSES | MATTER • A material cause, is the aspect which is determined by the material that composes the moving or changing things. • For a table, that might be wood; • For a statue, that might be bronze or marble. • For HIV, it might be the proteins and compounds that form the retrovirus.
  8. 8. ARISTOTELIAN CAUSES | FORM • A formal cause, is a change or movement caused by the arrangement, shape, or appearance of the thing changing or moving. • In other words, it describes the pattern or form which when present makes matter into a particular type of thing, which we recognize as being of that particular type
  9. 9. ARISTOTELIAN CAUSES | AGENT • An efficient or moving cause, consists of things apart from the thing being changed or moved, which interact so as to be an agency of the change or movement. • For example, the efficient cause of a table is a carpenter, or a person working as one. • In other words, it is simply the thing that brings something about. • Efficient causes are those generally describe by the word “cause” in modern English.
  10. 10. ARISTOTELIAN CAUSES | END • A final cause, or purpose, is that for the sake of which a thing is what it is. • For a seed, it might be an adult plant. • For a sailboat, it might be sailing. • For a ball at the top of a ramp, it might be coming to rest at the bottom. • We do not usually think that diseases have “final causes”
  11. 11. EXAMPLE: A SORE THROAT • With those sitting around you, can you define the “causes” of a sore throat? 1. Material cause: 2. Formal cause: 3. Efficient cause: 4. Final cause:
  12. 12. EXAMPLE: A SORE THROAT • With those sitting around you, can you define the causes of a sore throat? 1. Material cause: Biochemical, physical and psychological parts of a patient that allow disease to take hold. 2. Formal cause: The set of symptoms and signs observed during disease evolution, e.g., inflammation, pain, fever. 3. Efficient cause: The process which drives the disease, e.g., infection by a microbe. 4. Final cause: Evolution and reproduction of the disease.
  13. 13. • A conclusion about the presence of a health-related state or event and reasons for its existence. • Causal inferences provide a scientific basis for medical and public health action • Made with methods comprising lists of criteria or conditions applied to the results of scientific studies CAUSAL INFERENCE
  14. 14. • Direct causal association • No intermediate factor and is more obvious • Eliminating the exposure will eliminate the adverse health outcome • Example? • Indirect causal association • Involves one or more intervening factors • Often much more complicated • Example? TYPES OF CAUSAL ASSOCIATIONS
  15. 15. • Example 1 – A trauma to the skin results in a bruise or infection • Example 2 – Salmonella results in enteritis (inflammation of the small intestine) DIRECT CAUSAL ASSOCIATION
  16. 16. • Example 1 – Poor diet and stress may cause high blood pressure, which in turn causes heart disease • Example 2 – Early pregnancy may cause molecular changes that stabilize p53 (a tumor suppressor gene). With p53 stabilized, it remains functionally active longer to repair cumulative DNA damage and to prevent cellular proliferation induced by carcinogens. INDIRECT CAUSAL ASSOCIATION
  17. 17. RELATED TERMS • Risk factors • Risk behavior
  18. 18. RELATED TERMS | RISK FACTORS • A risk factor is any characteristic, attribute, or exposure of an individual that increases the likelihood of developing a HRSE.
  19. 19. RELATED TERMS | RISK BEHAVIOURS • An activity that places a person at increased risk for exposure or injury.
  20. 20. RELATED TERMS • Predisposing factors • Enabling factors • Precipitating factors • Reinforcing factors
  21. 21. RELATED TERMS | PREDISPOSING FACTORS • Factors or conditions already present that produce a susceptibility or disposition in a host to a disease or condition without actually causing it • Example 1 – Age • Example 2 – Immune status • Example 3 – Li-Fraumeni syndrome predisposes the person to a greater susceptibility of sarcomas, brain cancer, breast cancer, and leukemia • Other examples – Peoples’ knowledge, attitudes, beliefs, preferences, skills, and self-efficacy beliefs
  22. 22. RELATED TERMS | REINFORCING FACTORS • The factors that help aggravate and perpetuate behaviors, disease, conditions, disability, or death • Positive reinforcing factors • Social support, health education and economic assistance • Negative reinforcing factors • Negative peer influence or poor economic conditions
  23. 23. RELATED TERMS | ENABLING FACTORS • Antecedents to behaviors, disease, conditions, disability, or death that allow it to be realized • Services, living conditions, programs, societal supports, skills, and resources that facilitate a health outcome’s occurrence • Can also be a result of a lack of services or medical programs
  24. 24. RELATED TERMS | PRECIPITATING FACTORS • Factors essential to the development of diseases, conditions, injuries, disabilities, and death • An infectious agent • Lack of seat belt use in cars • Drinking and driving • Lack of helmet use on motorcycles
  25. 25. MEDIATORS & MODERATORS Odds Ratio Obesity Breast Cancer1.29 Physical Activity Mediation occurs when a third variable explains the association between the primary exposure and outcome of interest. Moderation occurs when a third variable interacts with the primary explanatory factor of interest and impacts the association with the outcome. Odds Ratio Drug Use 2.5 Income Education Odds Ratio 1.5 Income -> Drug Use Association for HS Dropouts Association for HS Grads Numbers are simulated, and do not reflect actual data. Odds Ratio Condomless Sex 1.71 Online Dating Intoxication During Sex Covariates are only related to the outcome.
  26. 26. CAUSAL INFERENCE Causal Webs Causal Pies A B C D A E F G A E C G Causal Criteria 2 3 6 4 5 7 8 9 1 Strength Consistency Specificity Temporality Biological Gradient Biological Plausibility Coherence Empiricism Analogy
  27. 27. • Webs are graphic, pictorial, or paradigm representations of complex sets of events or conditions caused by an array of activities connected to a common core or common experience or event. WEBS OF CAUSATION
  28. 28. • On a piece of paper, work with a small group of friends around you to create a web of causation for myocardial infarction (i.e., Heart Attack). ACTIVITY
  29. 29. MYOCARDIAL INFARCTION Myocardial Infarction Diet Exercise Smoking Stress Obesity Hyperlipidemia Coronary Atherosclerosis Coronary Occlusion Lack of Activity Increased catecholamine Thrombotic Activity Emotional Disturbance Hypertension Damage to Artery walls Aging
  30. 30. RELATED TERMS • Proximal • Distall • Salient
  31. 31. RELATED TERMS | PROXIMAL • Causes/Factors are said to be proximal when they are closer to the effect in the causal chain.
  32. 32. RELATED TERMS | DISTAL / UPSTREAM • Causes/Factors are said to be distal when they are “farther away” or “up stream.”
  33. 33. RELATED TERMS | SALIENT • Causes/Factors are said to be salient when they have a pronounced, or large effect. • Both proximal and distal factors can be salient.
  34. 34. REVIEW ACTIVITY • Based on the video in the next slide, map out the various causes. • After the video see if you and a partner can identify at least one example of each of the following causes for air quality. • Risk factors • Risk behaviors • Predisposing factors • Enabling factors • Precipitating factors • Reinforcing factors • Proximal • Distal • Salient
  35. 35. • Rothman’s causal pies explains the multifactorial nature of causation for many noninfectious diseases • The factors that cause the adverse health outcome are pieces of a pie, with the entire pie making up the sufficient cause for a health problem or one causal mechanism • Component causes – contributing factors to the cause of a health-related state or event • Component causes include agent, host factors, and environmental factors ROTHMAN’S CAUSAL PIES (1976)
  36. 36. A B C D A E F G A H I J Causal Mechanism Component Cause Necessary Cause: Components that are required to cause disease. Sufficient Cause: Component causes that always proceed disease, and when present cause disease. Disease G H F D No Disease ROTHMAN’S CAUSAL PIES
  37. 37. Poor Viral Control Exposure to HIV CCR5 Susceptibility Limited Access to ARTs Exposure to HIV is a necessary component cause for AIDS. Lack of access to antiretroviral therapy (ART), lack of natural resistance to HIV (i.e., CCR5-Δ32), and lack of natural viral control are component causes which while not necessary, may be important component causes which, along with exposure to HIV, contribute to onset of AIDS. e.g. ROTHMAN’S CAUSAL PIES
  38. 38. BRADFORD-HILL CAUSAL CRITERIA
  39. 39. CAUSAL CRITERIA | STRENGTH Factor 1 Factor 2 Factor 1 Factor 2 StrengthofCausalEvidence
  40. 40. CAUSAL CRITERIA | CONSISTENCY Low Accuracy Low Precision High Accuracy High Precision Low Accuracy High Precision High Accuracy Low Precision
  41. 41. CAUSAL CRITERIA | SPECIFICITY ① The cause must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms. ③ The cause should induce disease when introduced into a healthy organism. ② The cause must be isolated from a diseased organism and grown in pure culture ④ The cause must be reisolated from the experimental host and identified as the original causative agent. Robert Koch’s Postulates
  42. 42. CAUSAL CRITERIA | TEMPORALITY Cause Effect Time
  43. 43. CAUSAL CRITERIA | GRADIENT Has Disease No Disease Level of Exposure Probabilityof… Saturation Effect Threshold Effect
  44. 44. CAUSAL CRITERIA | PLAUSIBILITY
  45. 45. CAUSAL CRITERIA | COHERENCE Expert Opinion Ecological Studies Case Studies Cross-Sectional Surveys Case Control Studies Cohort Studies Randomized Controlled Trials Meta-Analyses & Reviews Epidemiological Studies StrengthofCausalEvidence
  46. 46. CAUSAL CRITERIA | EXPERIMENTAL • Multi-group • Treatment & Control • Placebo • Best Standard • Random Assignment • Blinded
  47. 47. CAUSAL CRITERIA | ANALOGY Vaccine A is Effective at Treating Pathogen A So, Vaccine B should be Effective at Treating Pathogen B
  48. 48. John Stuart Mills (1856) proposed three methods of hypothesis formulation in disease epidemiology: • Method of difference • Method of agreement • Method of concomitant variation METHODS OF HYPOTHESIS FORMULATION
  49. 49. • The frequency of disease occurrence is extremely different under different situations or conditions • If a risk factor can be identified in one condition and not in a second, it may be that factor, or the absence of it, that causes the disease METHOD OF DIFFERENCE
  50. 50. • If risk factors are common to a variety of different circumstances and the risk factors have been positively associated with a disease, then the probability of that factor being the cause is extremely high. METHOD OF AGREEMENT
  51. 51. • The frequency or strength of a risk factor varies with the frequency of the disease or condition • E.g., Increased numbers of children not immunized against measles causes the incidence rate for measles to go up. METHOD OF CONCOMITANT VARIATION
  52. 52. • Draws a conclusion about a population based on information from sampled data • Probability is used to indicate the level of reliability in the conclusion • The possibility that chance, bias, or confounding explain a statistical association should always be considered STATISTICAL INFERENCE
  53. 53. • Statistical association does not mean causal association • For example, ice cream consumption and murder are strongly correlated • Does eating ice cream make people want to kill or does killing result in a desire for ice cream? • The explanation may be that hot temperatures are related to both ice cream consumption and murder, and that it is the heat, not the ice cream, causally associated with murder STATISTICAL INFERENCE
  54. 54. • Confounding factors are always a threat in descriptive studies • Analytic epidemiologic studies are better for minimizing the threat of confounding • Nevertheless, descriptive studies are a good first step in the search for causes of health-related states or events CAUSALITY IN DESCRIPTIVE STUDIES
  55. 55. • Plotting health-related states or events over time can give the epidemiologist insights into probable determinants of disease • If a disease occurs only in the summer, then that is when the epidemiologist searches for causal factors CAUSALITY IN DESCRIPTIVE STUDIES
  56. 56. • Studies involving geographic comparisons of disease frequency between groups, states, countries, migration studies, and twin studies have further yielded important insights into the respective roles genetic and environmental forces have on disease. CAUSALITY IN DESCRIPTIVE STUDIES
  57. 57. • Next week is the midterm. • You can take it any time between 12:00am and 11:59pm. • There will be about 50 questions timed to take around 3 hours. • Make sure to give yourself the time you need to complete it. • Once the exam is started you must complete it. • We will not have class. • The week after you will meet with your groups to work on your projects. • There will be no lecture. THE END

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