Chance Is the association causal? RR = 7 Detectives in the Classroom – Investigation 3-3: Chance

Chance

Is the association

causal?

RR = 7

Detectives in the Classroom – Investigation 3-3: Chance

Hypotheses2

Is there an association?

4What should be done

to prevent the disease?

5Did the prevention

strategy work?

Where are we and where are we going?


1How is this disease

distributed?

What’s my hypothesis?

Did the exposure and the disease turn up

together?3Is the association

causal? Why did the exposure and the disease turn up

together?

What is a cause?

If an exposure causes an outcome, how can people be in cell b of a 2 x 2 table?

If an exposure causes an outcome, how can people be in cell c of a 2 x 2 table?

How does this apply to the “… cigarette smoking causes lung cancer …” label?

Review


1. Cause

2. Chance

3.

4.

5.

Review


Epi Talk

All the people in a particular group.

Population

Review


Epi Talk

A selection of people from a population.

Sample

Epi Talk


Epi Talk

Review

Inference

Process of predicting from what is observed in a sample to what is not observed in a population.

To generalize back to the source population.


Sample

Population

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

Observed

Not Observed

Review


Population

Deck of

100 cards


Population

a

25 cards

b

25 cards

c

25 cards

25 cards

d


Population

=

Population

a

25 cards

b c d

25 cards25 cards25 cards

=a b

c d

M&M’s

No M&M’s

FluNo

Flu


=

Population

a

25 cards

b c d


=M&M’s

No M&M’s

FluNo

Flu

2525

25 25

50

50

Total

Population


RiskEpi Talk

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.

Review


=

Population

=M&M’s

No M&M’s

FluNo

Flu

2525

25 25

50

50

Total

=

2525

25 25

50

50

Total

M&M’s

No M&M’s

FluNo

Flu

a

25 cards

b c d


Population


=

Population

=

2525

25 25

50

50

Total

a

25 cards

b c d


Risk

25 / 50 or 50%

25 / 50 or 50%

M&M’s

No M&M’s

FluNo

Flu

Population


Epi Talk

A way of showing the relationship between two risks.

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

Tells us the number of times one risk is larger or smallerthan another.

Relative Risk

Review


Sample


1

=

Population

a

25 cards

b c d


=

2525

25 25

50

50

Total

M&M’s

No M&M’s

FluNo

FluRisk Relative Risk

25 / 50 or 50 %

25 / 50 or 50 %

50 % / 50% = 1

Population


1

The risk of getting the flu is no more likely among those who ate M&M’s than among those who did not eat M&M’s.

Epi Teams


Population

25 cards

25 cards

25 cards

25 cards


Epi Talk

To occur accidentally.

To occur without design.

Chance

Epi Talk

A coincidence.


Chance


Chance


Population

Sample

Sample

b

Sample

of

20 cards25 cards25 cards25 cards25 cards


Population

Sample

b

Sample

of


10

10

Total

M&M’s

No M&M’s

FluNo

Flu

55

5 5

Sample


Population

Sample

b

Sample

of


10

10

Total

M&M’s

No M&M’s

FluNo

Flu

55

5 5

Risk

5 / 10 or 50 %

5 / 10 or 50 %

Sample


Sample


2

Population

Sample

b

Sample

of


10

10

Total

M&M’s

No M&M’s

FluNo

Flu

55

5 5

Risk

5 / 10 or 50 %

5 / 10 or 50 %

50 % / 50% = 1

Relative Risk

Sample 2


The risk of getting the flu is no more likely among those who ate M&Ms than among those who did not eat M&Ms.

b

Sample

of

20 cards

Total

M&M’s

No M&M’s

FluNo

Flu Risk

5 / 10 = 50 %

5 / 10 = 50 %

50 % / 50% = 1

Relative Risk

By Chance CDC

Sample


Sample


3

b

Sample

of

20 cards

Total

M&M’s

No M&M’s

FluNo

Flu Risk

5 / 10 = 50 %

5 / 10 = 50 %

50 % / 50% = 1

Relative Risk

By Chance CDC

By Chance

Sample 3


10

10

Total

M&M’s

No M&M’s

FluNo Flu

55

5 5

Risk

5 / 10 or 50 %

5 / 10 or 50 %

50 % / 50% = 1

Relative Risk

By Chance

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

Chance


Relative Risks

Greater than 1

Chance

Less than 1


Chance

Study Links Eating M&M’s To Increased Risk of Flu


Relative Risks

Chance

Greater than 1 Less than 1


Chance

Study Links Eating M&M’s To Decreased Risk of Flu


Relative Risks

Chance

Greater than 1 Less than 1

1

By ChanceBy Chance

25 cards25 cards25 cards25 cards


Sample


4

b

Sample

of

20 cards

Total

M&M’s

No M&M’s

FluNo

Flu Risk

5 / 10 = 50 %

5 / 10 = 50 %

50 % / 50% = 1

Relative Risk

Different Sample Sizes


50

Sample


5

b

Sample

of

20 cards

Total

M&M’s

No M&M’s

FluNo

Flu Risk

5 / 10 = 50 %

5 / 10 = 50 %

50 % / 50% = 1

Relative Risk



75

Sample


6

b

Sample

of

20 cards

Total

M&M’s

No M&M’s

FluNo

Flu Risk

5 / 10 = 50 %

5 / 10 = 50 %

50 % / 50% = 1

Relative Risk



99

Sample


7

Explanations for Finding an Association

Why would an exposure and an outcome turn up together?

1. Cause

2. Chance

3.

4.

5.

Study Links Eating M&M’s To Decreased Risk of Flu


Could the

association have occurred

by chance?

Explanations for Finding an Association

RR = 7


CDC

Investigation 3-3 has ended.

Chance


Documents

Chance Is the association causal? RR = 7 Detectives in the Classroom – Investigation 3-3: Chance