OVERVIEW OF STUDY DESIGN. COMMUNITY SURVEYS

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OVERVIEW OF STUDY DESIGN. COMMUNITY SURVEYS

• Nigel Paneth

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THREE MAJOR EPIDEMIOLOGIC STUDY TYPES

• COHORT STUDIES
• CASE-CONTROL STUDIES
• CROSS-SECTIONAL STUDIES

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COHORT STUDIES

• A. Sample selection by exposure
• Example following a group of workers exposed to
  asbestos and comparing their lung cancer rates
  to a group of workers not exposed to asbestos. If
  the non-exposed workers are matched to the
  exposed workers, the design is sometimes called
  exposure-control.
• B. Sample selection not by exposure Example
  following all workers, or a random sample of
  people in the community, determining their
  exposure to asbestos, then following them up for
  lung cancer.

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CASE-CONTROL STUDIES

• C. Sample selection by outcome Example workers
  with lung cancer are selected, and so are workers
  without lung cancer. Asbestos exposure is
  compared in the two groups.
• D. Sample selection not by outcome
  (virtually never done)
  Example All workers in a plant are assessed for
  presence or absence of lung cancer. The workers
  with and without lung cancer are compared for
  asbestos exposure.

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CROSS-SECTIONAL STUDIES

• E. Sample selection by exposure
• Example Workers with and without exposure to
  asbestos are compared for the simultaneous
  presence of lung cancer.
• F. Sample selection by outcome
•   Example Workers determined to have or not have
  lung cancer at a point in time are compared for
  simultaneous exposure to asbestos

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• G. Sample selection neither by outcome nor by
  exposure
•   Example All workers in a plant are
  simultaneously assessed both for asbestos
  exposure and lung cancer status.
• (Sampling schemes D, E and G are likely to be
  inefficient)

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THE MAIN DESCRIPTIVE STUDY IN EPIDEMIOLOGYTHE
COMMUNITY SURVEY

• A study which attempts to ascertain the
  frequency of a disease in a fixed geographic
  region (ideally) or in a group defined by a
  common membership, e.g. school-children. It
  usually assesses the frequency of disease in
  easily ascertained sub-groups, i.e. age, gender,
  geographic sub-units, ethnicity. etc. Often it
  is the first step in looking at risk factors for
  disease.

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THE COMMUNITY SURVEY

• PURPOSES
• 1. EXAMINE PREVALENCE (MORE RARELY,
  INCIDENCE)
• 2. ESTABLISH A BASELINE FOR FUTURE STUDIES
• 3. SET PUBLIC HEALTH PRIORITIES

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• 4. TARGET POPULATIONS AT RISK
• 5. NOTICE GEOGRAPHIC CLUSTERING
• 6. OBTAIN BASIC EPIDEMIOLOGY TIME, PLACE,
  PERSON (RACE, SEX, AND OTHER EASILY OBSERVED HOST
  FACTORS)
• 7. USUALLY NOT DRIVEN BY AN ETIOLOGIC
  HYPOTHESIS-DRIVEN.

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• II. METHODS
• 1. DIRECTIONALITY COMMONLY CROSS-SECTIONAL,
  THOUGH CAN INCORPORATE COHORT AND CASE-CONTROL
  COMPONENTS
• 2. SAMPLING GENERALLY POPULATION.
• 3. TIMING USUALLY CONCURRENT

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• III. TARGET CONDITIONS
• 1. SPECIFIC DISEASES
• 2. HANDICAPPING CONDITIONS
• 3. SYMPTOMS
• 4. RISK FACTORS FOR DISEASE
• 5. HAZARDOUS EXPOSURES

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• IV. TECHNIQUES
• 1. ACCESSING THE POPULATION
• A. HOUSE-TO-HOUSE
• B. TELEPHONE
• C. MAILED SURVEY

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• 2. ASSESSMENT
• A. SELF-REPORT
• B. PHYSICAL EXAMINATION
• C. LABORATORY TESTS
• D. COMBINATIONS