drugepi 4-1 introduction to interpreting associations module 4 overview context content area:...

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