Ecologic studies

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Ecologic studies

JF Boivin

S:\BOIVIN\695\Winter 2006\Ecologic studies (abbreviated).ppt (April 21, 2023)

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Outline

1. Examples

2. Definition

3. Ecologic fallacy

• Definition

• Valid ecologic study

• Rate difference varies

• Reference rate varies

4. Ecologic confounder

5. Types of ecologic exposures

6. Rationale for ecologic studies

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Percentage of children receiving measles-mumps-rubella immunization in second year of life and caseload of children with autism, by year of birth, California

(Dales et al., JAMA 2001)

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(Goodman DC, et al. NEJM 2002)

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Outline

1. Examples

2. Definition

3. Ecologic fallacy

• Definition







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Ecologic study

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Structure of an ecologic study: Counts

E+ E-

M1+

M1-

N1-N1+

D+

D-

?

?

?

?

Group 1

E+ E-

M2+

M2-

N2-N2+

D+

D-

?

?

?

?

Group 2

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Person-years

E+ E-

M1+

PY1T

D+

PY

?

PY1+

?

PY1-

Group 1

E+ E-

M2+

PY2T

D+

PY

?

PY2+

?

PY2-

Group 2

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Durkheim’s study

Protestant Other

10

1,000,000

Suicide

PY

?

300,000

?

700,000

Group 1 (provinces with protestant minority)

Protestant Other

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1,000,000

Suicide

PY

?

800,000

?

200,000

Group 2 (provinces with protestant majority)

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Actual study

? ?

Group 1

Group 2

? ?

? ?

Group 3

? ?

Group 4

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Outline

1. Examples

2. Definition

3. Ecologic fallacy

• Definition



• Reference rate varies across




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Ecologic fallacy

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No ecologic bias

E+ E-

32

20,000

D+

PY

24

12,000

8

8,000

Group 2 (Ontario)

IE = 200/100,000

Io = 100/100,000

RD = 100/100,000

RR = 2

Group rate = 32/20,000 =160/100,000

% exposure = 12,000/20,000=60%

Adapted from Rothman-Greenland Table 23-2

E+ E-

28

20,000

D+

PY

16

8,000

12

12,000

Group 1 (Québec)

IE

Io

RD

RR

Group rate =

% exposure =

15

No ecologic bias

110

120

140

130

150

160

170

180

190

200

100908070605040302010

RA

TE

(pe

r 10

0,00

0)

% EXPOSURE

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Ecologic bias(rate difference varies across groups)

E+ E-

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20,000

D+

PY

20

13,000

7

7,000

Group 2 (Ontario)

IE = 154/100,000

Io = 100/100,000

RD = 54/100,000

RR = 1.54

E+ E-

33

20,000

D+

PY

20

7,000

13

13,000

Group 1 (Québec)

IE = 286/100,000

Io = 100/100,000

RD = 186/100,000

RR = 2.86

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Ecologic bias

110

120

140

130

150

160

170

180

190

200

100908070605040302010

RA

TE

(pe

r 10

0,00

0)

% EXPOSURE

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Ecologic bias(reference rate varies across groups)

E+ E-

46

20,000

D+

PY

40

16,000

6

4,000

Group 2 (Ontario)

IE = 250/100,000

Io = 150/100,000

RD = 100/100,000

RR = 1.67

Group rate = 46/20,000 =230/100,000

% exposure = 16,000/20,000=80%

E+ E-

28

20,000

D+

PY

16

8,000

12

12,000

Group 1 (Québec)

IE = 200/100,000

Io = 100/100,000

RD = 100/100,000

RR = 2

Group rate = 28/20,000 =140/100,000

% exposure = 8,000/20,000 =40%

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Ecologic bias

0

100

150

200

250

100908070605040302010

RA

TE

(pe

r 10

0,00

0)

% EXPOSURE

IRR = = 5.5=IE

Io 50/100,000

275/100,000

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Outline

1. Examples

2. Definition

3. Ecologic fallacy

• Definition







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Outline

1. Examples

2. Definition

3. Ecologic fallacy

• Definition







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Aggregate exposure

Attributes of individuals that are summarized at the group level

Scientific interest may lie in:• Individual effect• Contextual effect

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Attributes of groups for which no distinct analog exists at the individual level

Everybody is exposed!

Intrinsically population-level exposure

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• Neighborhood social class as aggregate of individual social classes

Can differ from study subjects’ social class

• Neighborhood social class as contextual variable

Same contextual variable for all subjects

The variable is ecological, but the study is not!

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Outline

1. Examples

2. Definition

3. Ecologic fallacy

• Definition


• Rate difference varies across groups

• Reference rate varies across groups




Ecologic studies

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Transcript of Ecologic studies