ecologic studies n.
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Ecologic studies

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Ecologic studies

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  1. Ecologic studies JF Boivin S:\BOIVIN\695\Winter 2006\Ecologic studies (abbreviated).ppt (September 7, 2014)

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

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

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

  5. Ecologic study

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

  7. E+ E+ E- E- D+ D+ ? ? ? ? M1+ M2+ PY PY PY2+ PY1+ PY2- PY1- PY1T PY2T Person-years Group 1 Group 2

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

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

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

  11. Ecologic fallacy

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

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

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

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

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

  17. IE Io 275/100,000 IRR = = = 5.5 Ecologic bias 250 200 150 RATE (per 100,000) 100 0 10 20 30 40 50 60 70 90 100 80 % EXPOSURE 50/100,000

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

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

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

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

  22. 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!

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