the 2x2 table detectives in the classroom - investigation 2-1: the 2x2 table

The 2x2 Table

The 2x2 Table

Detectives in the Classroom - Investigation 2-1: The 2x2 Table

Where are we and where are we going?


1. How is this disease distributed and what hypotheses might explain that distribution?

2. Is there an association between the hypothesized cause and the disease?

3. Is the association causal?

4. What should individuals and society do when preventable causes of disease are found?

5. Did the prevention strategy work?

1How is this disease

distributed?Hypotheses

3Is the association

causal?

4What should be done

to prevent the disease?

5Did the prevention

strategy work?

Where are we and where are we going?

What’s my hypothesis?

2Is there

an association?

Did the exposure and the disease turn up

together?


Health-related conditions and behaviors are not distributed uniformly in a population. Each has a unique descriptive epidemiology that can be discovered by identifying how it is distributed in a population in terms of person, place, and time. Descriptive epidemiology provides clues for formulating hypotheses.

How is this disease distributed and what hypotheses might explain that distribution?

Review


Hypothesis

Testing Hypotheses


Formulate

Descriptive Epidemiology

Test

Analytical Epidemiology

Analytical EpidemiologyEpi Talk

A study designed to investigate hypothesized causal relationships.

Tries to determine why disease is occurring.

Tests hypotheses.

Epi Talk


Epidemiologist

Drug Company

Oily skin

AcneMed

AcneMed prevents

acne.

Acne

Oily skin causes acne.

Scenario


100 teenagers

Sample

Population

All Teenagers

Trial 1

10 teenagers had acne.

for 6 months

“AcneMed Prevents Acne.”



Epi Log Worksheet

AcneMed

AcneNo

Acne Total

10010 90

How is acne distributed

among the 100 teenagers

who took AcneMed?

Trial 1

10 Teenagers Had Acne


1

A measure of how often an event occurs in a defined population in a defined period of time. It consists of a numerator and a denominator.

Risk

The numerator is the number of people in the population who experience the event and the denominator is the total number of people in the population.

Population

Event

Denominator

Numerator

Express It in Numbers


Epi Talk


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.

AcneMed

AcneNo

Acne Total

10010

90100

10 or 10 %

Trial 1 Acne Risk

Express It in Numbers 2



Inference

100 teenagers

10/100 or 10%

Sample

Population

All Teenagers

Trial 1

Process of predicting from what is observed

Observed

Not Observed

to what is not observed.


InferenceEpi Talk

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.

Epi Talk


AcneMed

AcneNo

Acne Total

10010

90

Acne Risk

10010 or 10 %

Maybe they had acne when the experiment began.

Maybe they said they took AcneMed but did not.

Maybe they took AcneMed but not enough to prevent acne.

0 1000

0



If AcneMed prevents acne,

why did anyone get acne?

Shouldn’t the risk of acne

have been 0%?

AcneMed

AcneNo

Acne Total

10010

90

Acne Risk

10010 or 10 %

Maybe taking AcneMed does not prevent acne.

0 1000

0

What needs to be done?

Maybe those 90 teenagers would not have developed acne even if they had not taken AcneMed.



If AcneMed prevents acne,

why did anyone get acne?

Shouldn’t the risk of acne

have been 0%?

Control GroupEpi Talk

People who participate in a trial, but do not get the treatment.

Epi Talk


People whose results are compared to the group that was treated.


InferencePopulation

All Teenagers

Trial 1

Not Observed

100 teenagers

10/100 or 10%

Sample

Observed

? / 100 or ? % 100 teenagers

Sample

No AcneMed

AcneMed

Not Observed


Epi Teams


Experimental Group

AcneMed

AcneNo

Acne Total

10010

90

Acne Risk

10010 or 10 %

Trial 1


3

Control Group

AcneMed

AcneNo

Acne Total

10010

90

Acne Risk

10010 or 10 %

No AcneMed

100

Trial 1

?

100or ? %


3

ExposuresEpi Talk

Epi Talk


Factors with which individuals come in contact.

OutcomesEpi Talk

Epi Talk


All the possible results that occur because of exposure to a causal factor.

2 Rows, 2 Columns, 4 Cells

AcneMed

AcneNo

Acne Total

1009010

No AcneMed

100

a b

c d

2x2 Table


Exposure

Outcome / Disease

Exposed

DiseaseNo

Disease Total

Not Exposed

a b

dc

People who are exposed

a b

2x2 Table 4


Exposed

DiseaseNo

Disease Total

Not Exposed

a b

dc

People who are exposed and have the disease

a

2x2 Table 5


Exposed

DiseaseNo

Disease Total

Not Exposed

a b

dc

People who are not exposed and do not have the disease

d

2x2 Table 6


Exposed

DiseaseNo

Disease Total

Not Exposed

a b

dc

People who do not have the disease and are not exposed

d

2x2 Table 7


Exposed

DiseaseNo

Disease Total

Not Exposed

a b

dc

People who are not exposed

dc

2x2 Table 8


Exposed

DiseaseNo

Disease Total

Not Exposed

a b

dc

People who do not have the disease

d

b

2x2 Table 9


Exposed

DiseaseNo

Disease Total

Not Exposed

a b

dc

People who are exposed and do not have the disease

b

2x2 Table 10


Exposed

DiseaseNo

Disease Total

Not Exposed

a b

dc

People who have the disease

a

c

2x2 Table 11


Exposed

DiseaseNo

Disease Total

Not Exposed

a b

dc

c

People who are not exposed and have the disease

2x2 Table 12


EpidemiologyEpi Talk

The study of how and why diseases or other health-related conditions are distributed in a population the way they are; in other words, why some people get sick and others do not.

Review


Epidemiology

The study of how disease is distributed in populations and of the

exposures that cause that distribution.

AcneMed

AcneNo

Acne Total

1009010

No AcneMed

100

2x2 Table

How does this

definition apply

to the 2x2 table?

The 2x2 Table


AcneMed

AcneNo

Acne Total

1009010

No AcneMed

100

Epidemiology

The study of how disease is distributed in populations

and of the exposures that

cause that distribution.

2x2 Table

How does this

definition apply

to the 2x2 table?

The 2x2 Table


AcneMed

AcneNo

Acne Total

1009010

No AcneMed

100

2x2 Table Epidemiology

The study of how disease is distributed in populations

and of the exposures that

cause that distribution.

DiseaseNo

Disease

How does this

definition apply

to the 2x2 table?

Disease

The 2x2 Table


Disease

2x2 Table

How does this

definition apply

to the 2x2 table?

Epidemiology

The study of how disease is distributed in

populations and of the

exposures that cause that

distribution.

AcneMed

DiseaseNo

Disease Total

1009010

No AcneMed

100

Exposed

Not ExposedE

xpo

sure

sThe 2x2 Table


AcneMed

Total

No AcneMed

2x2 Table

How does this

definition apply

to the 2x2 table?

Epidemiology

The study of how disease is distributed in populations and of the

exposures that cause that distribution.

a b

c d

AcneNo

Acne

The 2x2 Table


When you can measure what you are speaking about, and express it in numbers, you know something about it. But when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind.

Lord Kelvin

How Is Acne Distributed?


Investigation 2-1 has ended.

The 2x2 Table


the 2x2 table detectives in the classroom - investigation 2-1: the 2x2 table

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