drugepi 4-1 introduction to interpreting associations module 4 overview context content area:...
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DrugEpi 4-1 Introduction to Interpreting Associations
Module 4 OverviewContext
Content Area: Interpretation of Epidemiological EvidenceEssential 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 AssociationsLesson 4-2: CausalityLesson 4-3: Chance Lesson 4-4: Bias Lesson 4-5: ConfoundingLesson 4-6: Reverse Time Order Lesson 4-7: Weighing the Evidence
DrugEpi 4-1 Introduction to Interpreting Associations
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.
DrugEpi 4-1 Introduction to Interpreting Associations
Where are we?
Essential Questions Enduring Understandings
1. How is this disease distributed?
Health-related conditions and behaviors are not distributed uniformly in a population. They have unique distributions that can be described by how they are distributed in terms of person, place, and time.
2. What hypotheses might explain the distribution of disease?
Clues for formulating hypotheses can be found by observing the way a health-related condition or behavior is distributed in a population.
3. Is there an association between the hypothesized cause and the disease?
Causal hypotheses can be tested by observing exposures and diseases of people as they go about their daily lives. Information from these observational studies can be used to make and compare rates and identify associations.
4. Is the association causal?
Causation is only one explanation for an association between an exposure and a disease. Because observational studies are complicated by factors not controlled by the observer, other explanations also must be considered.
5. What should be done when preventable causes of disease are found?
Policy decisions are based on more than the scientific evidence. Because of competing values - social, economic, ethical, environmental, cultural, and political factors may also be considered.
DrugEpi 4-1 Introduction to Interpreting Associations
Concept Map So Far . . .
The Science of Public Health: Epidemiology
Hypothesis
Total Risk Relative Risk
a b
c d
or %
or %Exposure
Outcome
?Turned Up Together
Healthy People
-
Healthy People
E
E
DZ
DZ
DZ
DZ
DrugEpi 4-1 Introduction to Interpreting Associations
Concept Map . . Where We Are Going . . .
Hypothesis
Total Risk Relative Risk
a b
c d
or %
or %
ExposureOutcom
e
?Turned Up Together
Healthy People
-
Healthy People
E
E
DZ
DZ
DZ
DZ
Person, Place, Time
Surveillance
Testing HypothesesInterpretation?
DrugEpi 4-1 Introduction to Interpreting Associations
What do we mean when we say that there is an association between two things?
Associated
Tied Related
Linked
Things that are associatedare linked in some way that makes them
turn up together.
Review - Definition of an Association
Optional - Use if needed for a concept connection
DrugEpi 4-1 Introduction to Interpreting Associations
Outcome
Outcome
a b
c d
Exposure
No
Exposure
No Outcome
Exp
osu
re
Review - Showing that Things Turn Up Together
Optional - Use if needed for a concept connection
DrugEpi 4-1 Introduction to Interpreting Associations
To give the meaning of, explain, or make clear.
Interpret
Study Interpretation
DrugEpi 4-1 Introduction to Interpreting Associations
Suicide Higher in Areas with Guns
Smoking Linked to Youth Eating Disorders
Snacks Key to Kids’ TV- Linked Obesity: China Study
Family Meals Are Good for Mental Health
Lack of High School Diploma Tied to US Death
Rate
Study Links
Spanking to
Aggression
Breakfast Each Day May Keep Colds Away
Study Concludes: Movies Influence
Youth Smoking
Study Links Iron
Deficiency to Math
Scores
Kids Who Watch R-Rated Movies More Likely to Drink, Smoke
Pollution Linked with Birth Defects in US Study
Depressed Teens More Likely to Smoke
Review - Things That Turn Up Together
DrugEpi 4-1 Introduction to Interpreting Associations
IS ASSOCIATE
D WITHIN
Is the Association Causal?
DrugEpi 4-1 Introduction to Interpreting Associations
Suicide Higher in Areas with Guns
Family Meals Are Good for Mental Health
Lack of High School Diploma Tied to US Death
Rate
Study Links
Spanking to
Aggression
Study Concludes: Movies Influence
Youth Smoking
Study Links Iron
Deficiency to Math
Scores
Kids Who Watch R-Rated Movies More Likely to Drink, Smoke
Pollution Linked with Birth Defects in US Study
Possible Reasons Why Things Turn Up Together
1. Cause
2. Chance
3. Bias
4. Confounding
5. Reverse Time Order
Snacks Key to Kids’ TV- Linked Obesity: China
Study
Depressed Teens More
Likely to Smoke
DrugEpi 4-1 Introduction to Interpreting Associations
Exercise in Interpreting an Association
Association Found Between Coffee and Pancreatic Cancer
DrugEpi 4-1 Introduction to Interpreting Associations
1. Cause
2.
3.
4.
5.
Possible Explanations for Finding an Association
DrugEpi 4-1 Introduction to Interpreting Associations
Anything that produces an effect
Cause
Explanation 1 - Causal
DrugEpi 4-1 Introduction to Interpreting Associations
An exposure that increases the likelihood of a specific outcome.
Risk Factor
Explanation 1 - Causal
DrugEpi 4-1 Introduction to Interpreting Associations
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.”
Explanation 1 - Causal
DrugEpi 4-1 Introduction to Interpreting Associations
1. Cause
2. Chance
3.
4.
5.
Possible Explanations for Finding an Association
DrugEpi 4-1 Introduction to Interpreting Associations
Chance
Explanation 2 - Chance
To occur accidentally
To occur without design
A coincidence
DrugEpi 4-1 Introduction to Interpreting Associations
1. Cause
2. Chance
3. Bias
4.
5.
Possible Explanations for Finding an Association
DrugEpi 4-1 Introduction to Interpreting Associations
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.
Explanation 5 - Study Bias
Leon Gordis, Epidemiology, 3rd Edition, Elsevier Saunders, 2004.
DrugEpi 4-1 Introduction to Interpreting Associations
1. Cause
2. Chance
3. Bias
4. Confounding
5.
Possible Explanations for Finding an Association
DrugEpi 4-1 Introduction to Interpreting Associations
Confounding
Explanation 3 - 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.
DrugEpi 4-1 Introduction to Interpreting Associations
Confounding
Explanation 3 - 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
DrugEpi 4-1 Introduction to Interpreting Associations
Cause
Association Cause
XObserved
Not Observed Confounder
Match-Carrying
Lung Cancer
Diagram of Confounding
Smoking
DrugEpi 4-1 Introduction to Interpreting Associations
1. Cause
2. Chance
3. Bias
4. Confounding
5. Reverse Time Order
Possible Explanations for Finding an Association
DrugEpi 4-1 Introduction to Interpreting Associations
Egg Chicken
Outcome
Explanation 4 - Reverse Time Order
Hypothesized Exposure
?
DrugEpi 4-1 Introduction to Interpreting Associations
Hypothesized Exposure
Outcome
Explanation 4 - Reverse Time Order
Playing Violent Video Games
Violent Behavior
DrugEpi 4-1 Introduction to Interpreting Associations
1. Cause
2. Chance
3. Bias
4. Confounding
5. Reverse Time Order
The Science of Public Health: Epidemiology
Possible Explanations for Finding an Association
To reiterate . . .
DrugEpi 4-1 Introduction to Interpreting Associations
... the study of the distribution and determinants of health-related states or events in specified populations and the application of this study to the control of health problems.
(Gordis, 2004)
Review - Definition and Purpose of Epidemiology
How do the five possible explanations relate to the idea that epidemiology studies are done for purposes of
eventually controlling health problems?
DrugEpi 4-1 Introduction to Interpreting Associations
Outcome
If an association was causal, ….
Exposure XX… and you avoided or eliminated the hypothesized
cause, what would happen to the outcome?
causal, ….
?
Possible Explanations for Finding an Association
DrugEpi 4-1 Introduction to Interpreting Associations
Outcome
If an association was found due to chance, ….
Exposure
found due to chance, ….
Possible Explanations for Finding an Association
X… and you avoided or eliminated the hypothesized
cause, what would happen to the outcome?
?
DrugEpi 4-1 Introduction to Interpreting Associations
Outcome
If an association was found due to bias, ….
Exposure
?
found due to bias, ….
Possible Explanations for Finding an Association
X… and you avoided or eliminated the hypothesized
cause, what would happen to the outcome?
DrugEpi 4-1 Introduction to Interpreting Associations
Outcome
If the association was found due to confounding, ….
Exposure
Unobserved Exposure
Possible Explanations for Finding an Association
X… and you avoided or eliminated the hypothesized
cause, what would happen to the outcome?
?
found due to confounding, ….
DrugEpi 4-1 Introduction to Interpreting Associations
Exposure Outcome
If an association was found due to reversed time-order, ….found due to reverse time order, ….
Possible Explanations for Finding an Association
X… and you avoided or eliminated the hypothesized
cause, what would happen to the outcome?
?
DrugEpi 4-1 Introduction to Interpreting Associations
• 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
Big Ideas
DrugEpi 4-1 Introduction to Interpreting Associations
Exercise in Interpreting an Association
Association Found Between Coffee and Pancreatic Cancer
Optional
DrugEpi 4-1 Introduction to Interpreting Associations
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.
Always Remember
DrugEpi 4-1 Introduction to Interpreting Associations
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.
Don’t Forget
DrugEpi 4-1 Introduction to Interpreting Associations
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.
Re-Cap
DrugEpi 4-1 Introduction to Interpreting Associations
Next Lesson
Causality
SURGEON GENERAL’S WARNING:Smoking Causes Lung Cancer, Heart Disease, Emphysema, and May Complicate Pregnancy