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:
Lesson 4-2:
Lesson 4-3:
Lesson 4-4:
Lesson 4-5:
Lesson 4-6:
Lesson 4-7:
Introduction to Interpreting Associations
Causality
Chance
Bias
Confounding
Reverse Time Order
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 . . .
DZ
Hypothesis
E
DZ
Healthy
Healthy
People
People
DZ
E
-
Total
DZ
Risk
Relative Risk
or
%
or
%
?
a b
c d
Exposure
Outcom
e
Turned Up Together
The Science of Public Health: Epidemiology
DrugEpi 4-1 Introduction to Interpreting Associations
Concept Map . . Where We Are Going . . .
Person, Place, Time
DZ
E
DZ
Healthy
Healthy
People
People
DZ
E
-
Total
DZ
Risk
or
Relative Risk
%
a b
?
Exposure
c d
or
%
Outcom
e
Turned Up Together
DrugEpi 4-1 Introduction to Interpreting Associations
Review - Definition of an Association
Tied
Related
Associated
Linked
What do we mean when we say that
there is an association between two things?
Things that are associated
are linked in some way
that makes them turn up together.
DrugEpi 4-1 Introduction to Interpreting Associations
Review - Showing that Things Turn Up Together
Outcome
Exposure
Outcome
No
Outcome
Exposure
a b
No
Exposure
DrugEpi 4-1 Introduction to Interpreting Associations
c d
Study Interpretation
Interpret
To give the meaning of, explain, or make clear.
DrugEpi 4-1 Introduction to Interpreting Associations
Review - Things That Turn Up Together
Suicide Higher in
Areas with Guns
Smoking Linked to Youth
Family Meals Are
Eating Disorders
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
DrugEpi 4-1 Introduction to Interpreting Associations
Is the Association Causal?
IS
ASSOCIATED
WITH
DrugEpi 4-1 Introduction to Interpreting Associations
I
N
Possible Reasons Why Things Turn Up Together
Suicide Higher in
Areas with Guns
1.
Cause
Study Links
Iron Deficiency
to Math Scores
2.
Chance
3.
Bias
4.
Confounding
Lack of High School
Diploma Tied to
US Death Rate
Family Meals Are
Good for Mental Health
Study Concludes:
Movies Influence
Youth Smoking
Study Links
Spanking
to Aggression
Depressed
Teens More
Likely to
Smoke
Snacks Key to
Kids’ TV- Linked
5. Reverse
Obesity: China
Time Order
Study
Pollution Linked with Birth Defects in US Study
Kids Who Watch R-Rated Movies More Likely to Drink, 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
Possible Explanations for Finding an Association
1. Cause
2.
3.
4.
5.
DrugEpi 4-1 Introduction to Interpreting Associations
Explanation 1 - Causal
Cause
Anything that produces an effect
DrugEpi 4-1 Introduction to Interpreting Associations
Explanation 1 - Causal
Risk Factor
An exposure that increases
the likelihood of a specific outcome.
DrugEpi 4-1 Introduction to Interpreting Associations
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.”
DrugEpi 4-1 Introduction to Interpreting Associations
Possible Explanations for Finding an Association
1.
Cause
2.
Chance
3.
4.
5.
DrugEpi 4-1 Introduction to Interpreting Associations
Explanation 2 - Chance
Chance
To occur accidentally
To occur without design
A coincidence
DrugEpi 4-1 Introduction to Interpreting Associations
Possible Explanations for Finding an Association
1.
Cause
2.
Chance
3.
Bias
4.
5.
DrugEpi 4-1 Introduction to Interpreting Associations
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.
DrugEpi 4-1 Introduction to Interpreting Associations
Possible Explanations for Finding an Association
1.
Cause
2.
Chance
3.
Bias
4.
Confounding
5.
DrugEpi 4-1 Introduction to Interpreting Associations
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.
DrugEpi 4-1 Introduction to Interpreting Associations
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
DrugEpi 4-1 Introduction to Interpreting Associations
Diagram of Confounding
Smoking
MatchCarrying
DrugEpi 4-1 Introduction to Interpreting Associations
X
Lung Cancer
Possible Explanations for Finding an Association
DrugEpi 4-1 Introduction to Interpreting Associations
1.
Cause
2.
Chance
3.
Bias
4.
Confounding
5.
Reverse Time Order
Explanation 4 - Reverse Time Order
Egg
Hypothesized
Exposure
DrugEpi 4-1 Introduction to Interpreting Associations
Chicken
?
Outcome
Explanation 4 - Reverse Time Order
Hypothesized
Exposure
Playing Violent
Video Games
DrugEpi 4-1 Introduction to Interpreting Associations
Outcome
Violent
Behavior
Possible Explanations for Finding an Association
To reiterate . . .
1.
Cause
2.
Chance
3.
Bias
4.
Confounding
5.
Reverse Time Order
The Science of Public Health: Epidemiology
DrugEpi 4-1 Introduction to Interpreting Associations
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 control of
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?
DrugEpi 4-1 Introduction to Interpreting Associations
Possible Explanations for Finding an Association
X
Exposure
DrugEpi 4-1 Introduction to Interpreting Associations
X
?
Outcome
Possible Explanations for Finding an Association
X
Exposure
DrugEpi 4-1 Introduction to Interpreting Associations
?
Outcome
Possible Explanations for Finding an Association
X
Exposure
DrugEpi 4-1 Introduction to Interpreting Associations
?
Outcome
Possible Explanations for Finding an Association
Unobserved
Exposure
X
Exposure
DrugEpi 4-1 Introduction to Interpreting Associations
?
Outcome
Possible Explanations for Finding an Association
X
Exposure
DrugEpi 4-1 Introduction to Interpreting Associations
?
Outcome
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
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
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.
DrugEpi 4-1 Introduction to Interpreting Associations
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.
DrugEpi 4-1 Introduction to Interpreting Associations
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.
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
DrugEpi 4-1 Introduction to Interpreting Associations