DrugEpi 4-3 Chance

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 4-3 Chance

Module 4 - Interpretation of Epidemiological Evidence

Lesson 4-3 Chance

Content

• A class exercise with 100 cards to illustrate

“chance” as a possible explanation for an association

Big Ideas

• When an association is found, several possible explanations must be considered, including the possibility that the association is due to chance

• The larger the sample size, the less likely that an observed association is due to chance

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 4-3 Chance

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 4-3 Chance

Chance

Is the association due

to chance?

1. Cause

2. Chance

3.

4.

5.

DrugEpi 4-3 Chance

Population

All the people in a particular group.

Review

DrugEpi 4-3 Chance

Sample

A selection of people from a population

Review

DrugEpi 4-3 Chance

Sample

Population

Process of predicting from what is observedto what is not observed.

(Observed)

(Not Observed)

Review

Inference

DrugEpi 4-3 Chance

Deck of

100 cards

Population

DrugEpi 4-3 Chance

a

25 cards

b

25 cards

c

25 cards

25 cards

d

Population

DrugEpi 4-3 Chance

=

Population

a b c d

Population

Exposure = eating chocolate

Outcome = trying marijuana

DrugEpi 4-3 Chance

=

Population

a

25 cards

b c d

25 cards25 cards25 cards

=a b

c d

Odd #

Even #

No Marijuana

No Marijuana

Population

Total

DrugEpi 4-3 Chance

Exposed

Not Exposed

OutcomeNo

Outcome Total

Review - The 2x2 Table

The 2x2 table

can express

relationships

between exposure

and outcome

Optional

DrugEpi 4-3 Chance

The 2x2 table is a tool used to express the numbers of people

with and without the exposure and with and without

the outcome.

Review - The 2x2 Table

Optional

DrugEpi 4-3 Chance

A cross-classification of data where categories of one

variable are presented in rows and categories of another variable

are presented in columns.

Review - Another Way To Say . . .

Optional

DrugEpi 4-3 Chance

TotalOutcomeNo

Outcome

Exposed

Not Exposed

Exposure

Outcome / Disease

a b

c d

Review - The 2x2 Table

Are there controls in this

2x2 table?

If yes, where are they?

Optional

DrugEpi 4-3 Chance

=

Population

a

25 cards

b c d

25 cards25 cards25 cards

= 2525

25 25

50

50

Total

Odd #

Even #

No Marijuana

No Marijuana

Population

DrugEpi 4-3 Chance

=

Population

=M&M’s

No M&M’s

FluNo

Flu

2525

25 25

50

50

Total

=

2525

25 25

50

50

Total

a

25 cards

b c d

25 cards25 cards25 cards

Odd #

Even #

No Marijuana

No Marijuana

Population

DrugEpi 4-3 Chance

Relative Risk

A way of showing the relationship between two risks

Tells us the number of times one risk is larger or smaller

than another

Calculated by dividing the risk of an outcome in one group by the risk of the outcome

in another group

Review

Risk

A measure of how often an event occurs in a defined group of people in a defined period of time

The likelihood of developing a disease

DrugEpi 4-3 Chance

=

Population

=

2525

25 25

50

50

Total

a

25 cards

b c d

25 cards25 cards25 cards

Risk

25 / 50 or 50%

25 / 50 or 50%

Odd #

Even #

No Marijuana

No Marijuana

Population

DrugEpi 4-3 Chance

=

Population

a

25 cards

b c d

25 cards25 cards25 cards

=

2525

25 25

50

50

Total Risk Relative Risk

25 / 50 or 50 %

25 / 50 or 50 %50 % / 50% = = 1

50 %

50 %

____Odd #

Even #

No Marijuana

No Marijuana

Population

DrugEpi 4-3 Chance

25 cards

25 cards

25 cards

25 cards

Population

DrugEpi 4-3 Chance

Definition

Chance

To occur accidentally

To occur without design

A coincidence

DrugEpi 4-3 Chance

Chance

DrugEpi 4-3 Chance

Chance

DrugEpi 4-3 Chance

Population

Sample

b

Sample

of

20 cards25 cards25 cards25 cards25 cards

Sample

DrugEpi 4-3 Chance

Population

Sample

b

Sample

of

20 cards25 cards25 cards25 cards25 cards

10

10

Total

55

5 5Chocolate

No Chocolate

No Marijuana

No Marijuana

Sample

DrugEpi 4-3 Chance

Population

Sample

b

Sample

of

20 cards25 cards25 cards25 cards25 cards

10

10

Total

55

5 5

Risk

5 / 10 or 50 %

5 / 10 or 50 %Chocolate

No Chocolate

No Marijuana

No Marijuana

Sample

DrugEpi 4-3 Chance

Population

Sample

b

Sample

of

20 cards25 cards25 cards25 cards25 cards

10

10

Total

55

5 5

Risk

5 / 10 or 50 %

5 / 10 or 50 %Chocolate

No Chocolate

No Marijuana

No Marijuana

Sample

Relative Risk

50 % / 50% = = 1.050 %

50 %

____

DrugEpi 4-3 Chance

b

Sample

of

20 cards

TotalRisk

5 / 10 = 50 %

5 / 10 = 50 %

50 1

Relative Risk

By Chance CDC

% ___

%

= Chocolate

No Chocolate

No Marijuana

No Marijuana

Sample

DrugEpi 4-3 Chance

10

10

Total

55

5 5

Risk

5 / 10 or 50 %

5 / 10 or 50 %

Relative Risk

How many students picked a sample with 5 people in each cell?

= 1.050 %

50 %

____

Chocolate

No Chocolate

No Marijuana

No Marijuana

Chance

By Chance

DrugEpi 4-3 Chance

Worksheet

DrugEpi 4-3 Chance

Relative Risks

Greater than 1.0 Less than 1.0

Chance

DrugEpi 4-3 Chance

Study of High School Students

Links Chocolate-Eating Habit

to a Higher Risk

of Trying Marijuana

In the News

DrugEpi 4-3 Chance

Relative Risks

Greater than 1.0 Less than 1.0

Possible Explanations for Finding an Association

DrugEpi 4-3 Chance

In the News

Study of High School Students

Links Eating Chocolate

to a Lower Risk

of Trying Marijuana

DrugEpi 4-3 Chance

Relative Risks

Greater than 1.0 Less than 1.0

By ChanceBy Chance

25 cards25 cards25 cards25 cards

ChanceRange?20

cards

DrugEpi 4-3 Chance

b

Sample

of

20 cards

TotalRisk

5 / 10 = 50 %

5 / 10 = 50 %

50

Relative Risk

50

%___

%

=Odd #

Even #

No Marijuana

No Marijuana

Different Sample Sizes

DrugEpi 4-3 Chance

Relative Risks

Greater than 1.0 Less than 1.0

By ChanceBy Chance

25 cards25 cards25 cards25 cards

Chance

50 card

s

Range?

DrugEpi 4-3 Chance

b

Sample

of

20 cards

TotalRisk

5 / 10 = 50 %

5 / 10 = 50 %

50

Relative Risk

75

%___

%

=Odd #

Even #

No Marijuana

No Marijuana

Different Sample Sizes

DrugEpi 4-3 Chance

Relative Risks

Greater than 1.0 Less than 1.0

By ChanceBy Chance

25 cards25 cards25 cards25 cards

Chance

75 card

s

Range?

DrugEpi 4-3 Chance

b

Sample

of

20 cards

TotalRisk

5 / 10 = 50 %

5 / 10 = 50 %

50 1

Relative Risk

99

%___

%

=Odd #

Even #

No Marijuana

No Marijuana

Different Sample Sizes

DrugEpi 4-3 Chance

Review Results

DrugEpi 4-3 Chance

Chance

Could the association have

occurred by chance?

1. Cause

2. Chance

3.

4.

5.

DrugEpi 4-3 Chance

Big Ideas in this Lesson (4-3)

• When an association is found, several possible explanations must be considered, including the possibility that the association is due to chance

• The larger the sample size, the less likely that an observed association is due to chance

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 4-3 Chance

   

 

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Bias