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Epidemiology Kept Simple. Ch 11: Observational Studies. Observational Designs . Cross-sectional : Sample population, no follow-up of individuals  compare disease experience of exposure groups (§11.2 and §11.3)

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epidemiology kept simple

Epidemiology Kept Simple

Ch 11: Observational Studies

Ch 11: Observational Designs

observational designs
Observational Designs
  • Cross-sectional: Sample population, no follow-up of individuals  compare disease experience of exposure groups (§11.2 and §11.3)
  • Cohort: closed population with individual follow-up over time  compare disease experience of exposure groups (§11.4)
  • Case-control: all cases and a sample of non-cases from population  compare exposure experience (§11.5)

Ch 11: Observational Designs

cross sectional designs
Cross-Sectional Designs
  • Recall distinction between longitudinal and cross-sectional observations
  • Recall the distinction between individual and aggregate units of observation
  • Cross-sectional design with aggregate unit of observation≡ ecological design
  • Cross-sectional data with individual units ≡ cross-sectional survey

Ch 11: Observational Designs

example ecological data
Example: Ecological Data

Unit of observation = geographic region

Exposure = Cig1930 = cigarettes per capita, 1930

Disease = Mortal = lung cancer mortality per 100,000 p-yrs, 1950

Ch 11: Observational Designs

example ecological data5
Example: Ecological Data

r = 0.74

Ch 11: Observational Designs

11 4 c ohort studies
§11.4 Cohort Studies
  • Recruit cohort
  • Classify individual as exposed or non-exposed
  • Follow exposed and non-exposed sub-cohorts to determine incidence

exposed

sub-cohort

Incidence1

Closed

population

RR or RD

RR or RD

RR or RD

RR or RD

non-exposed

sub-cohort

Incidence0

Ch 11: Observational Designs

british doctors cohort

50% heavy smokers survived to 70

British Doctors Cohort

80% of nonsmoker survived to age 70

Source: Doll, R., Peto, R., Wheatley, K., Gray, R., & Sutherland, I. (1994). Mortality in relation to smoking: 40 years\' observations on male British doctors. British Medical Journal, 309(6959), 901-911.

Ch 11: Observational Designs

example historical cohort
Example: Historical Cohort
  • Historical info on exposure to aniline dyes (from work records) were used to compile exposed and non-exposed worker cohorts
  • Retrospective data from death certificates on bladder cancer occurrence
  • Result: bladder cancer occurrence was 100 times as frequent in aniline-exposed cohort
  • Figure shows induction time between exposure onset and bladder CA occurrence

Ch 11: Observational Designs

case control studies
Case-Control Studies
  • Identify population cases
  • Randomly select non-cases (“controls”)
  • Compare exposure histories in cases & controls

All cases

Exposure histories

Population

Odds Ratio

Sample non-cases

Exposure histories

Ch 11: Observational Designs

case control
Case-Control

Cross-tabulate disease and exposure status

of cases and controls

Calculate:

Ch 11: Observational Designs

interpretation of the odds ratio
Interpretation of the Odds Ratio
  • When the disease is rare, interpret the OR as if it were an RR
  • The illustrative OR of 9.3 suggests that tampon users had 9.3 times the risk as non-tampon users
  • [The suspected brand of tampon has since been removed from the market]

Ch 11: Observational Designs

multiple levels of exposure historical example wynder graham 1950 p 212
Multiple Levels of ExposureHistorical Example: (Wynder & Graham, 1950, p. 212)

Exposure may be measured at various levels. In this historical example, smoking is classified into 6 levels. To analyze the table, break-up it up into five separate 2-by-2 tables with each table referencing the nonexposed group as follows:

Ch 11: Observational Designs

longitudinal designs
Longitudinal Designs

Ch 11: Observational Designs

longitudinal designs15
Longitudinal Designs

Ch 11: Observational Designs

end of hs 261 presentation

End of HS 261 Presentation

Ch 11: Observational Designs

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