1. Ecologic studies JF Boivin
S:\BOIVIN\695\Winter 2006\Ecologic studies (abbreviated).ppt (August 28, 2018)

2. Outline Examples Definition Ecologic fallacy Valid ecologic study
Rate difference varies
Reference rate varies
4. Ecologic confounder
Types of ecologic exposures
Rationale for ecologic studies

3. 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)

5. (Goodman DC, et al. NEJM 2002)

6. Outline Examples Definition Ecologic fallacy Valid ecologic study
Rate difference varies
Reference rate varies
4. Ecologic confounder
Types of ecologic exposures
Rationale for ecologic studies

7. Ecologic study

8. Structure of an ecologic study: Counts
Group 1 E+ E-
M1+
M1-
N1-
N1+ D+ D- ?
Group 2 E+ E-
M2+
M2-
N2-
N2+ D+ D- ?

9. Person-years Group 1 Group 2 E+ E- M1+ PY1T D+ PY ? PY1+ PY1- E+ E-

10. Durkheim’s study Protestant Other 10 1,000,000 Suicide PY ? 300,000
700,000
Group 1 (provinces with protestant minority)
Protestant
Other 20
1,000,000
Suicide PY ?
800,000
200,000
Group 2 (provinces with protestant majority)

11. Actual study
Group 1 ?
Group 2 ?
Group 3 ?
Group 4 ?

12. Outline Examples Definition Ecologic fallacy Valid ecologic study
Rate difference varies
Reference rate varies across
Ecologic confounder
Types of ecologic exposures
Rationale for ecologic studies

13. Ecologic fallacy

14. No ecologic bias Group 1 (Québec) Group 2 (Ontario) E+ E- 28 20,000 D+PY 16
8,000 12
12,000 IE Io RD RR
% exposure =
Group rate =
Group 2 (Ontario) E+ E- 32
20,000 D+ PY 24
12,000 8
8,000 IE =
200/100,000 Io =
100/100,000 RD =
100/100,000 RR 2
% exposure =
12,000/20,000
60%
Group rate =
32/20,000
160/100,000
Adapted from Rothman-Greenland Table 23-2

15. No ecologic bias RATE (per 100,000) % EXPOSURE 200 190 180 170 160 150
140
130
120
110 10 20 30 40 50 60 70 80 90
100
% EXPOSURE

16. Ecologic bias (rate difference varies across groups)
Group 1 (Québec) E+ E- 33
20,000 D+ PY 20
7,000 13
13,000 IE =
286/100,000 Io =
100/100,000 RD =
186/100,000 RR
2.86
Group 2 (Ontario) E+ E- 27
20,000 D+ PY 20
13,000 7
7,000 IE =
154/100,000 Io =
100/100,000 RD =
54/100,000 RR
1.54

17. Ecologic bias RATE (per 100,000) % EXPOSURE 200 190 180 170 160 150
140
130
120
110 10 20 30 40 50 60 70 80 90
100
% EXPOSURE

18. Ecologic bias (reference rate varies across groups)
Group 1 (Québec) E+ E- 28
20,000 D+ PY 16
8,000 12
12,000 IE =
200/100,000 Io =
100/100,000 RD =
100/100,000 RR 2
% exposure =
8,000/20,000
40%
Group rate =
28/20,000
140/100,000
Group 2 (Ontario) E+ E- 46
20,000 D+ PY 40
16,000 6
4,000 IE =
250/100,000 Io =
150/100,000 RD =
100/100,000 RR
1.67
% exposure =
16,000/20,000
80%
Group rate =
46/20,000
230/100,000

19. Ecologic bias RATE (per 100,000) % EXPOSURE = IE Io 275/100,000 IRR =
250
200
150
RATE (per 100,000)
100 10 20 30 40 50 60 70 80 90
100
% EXPOSURE = IE Io
275/100,000
IRR = =
5.5
50/100,000

20. Outline Examples Definition Ecologic fallacy Valid ecologic study
Rate difference varies
Reference rate varies
Ecologic confounder
Types of ecologic exposures
Rationale for ecologic studies

21. Outline Examples Definition Ecologic fallacy Valid ecologic study
Rate difference varies
Reference rate varies
Ecologic confounder
Types of ecologic exposures
Rationale for ecologic studies

22. Aggregate exposure
Attributes of individuals that are summarized at the group level
Scientific interest may lie in:
Individual effect
Contextual effect

23. Intrinsically population-level exposure
Attributes of groups for which no distinct analog exists at the individual level
Everybody is exposed!

25. 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!

27. Outline Examples Definition Ecologic fallacy Valid ecologic study
Rate difference varies across groups
Reference rate varies across groups
Ecologic confounder
Types of ecologic exposures
Rationale for ecologic studies