OVERVIEW OF STUDY DESIGN. COMMUNITY SURVEYS Nigel Paneth

THREE MAJOR EPIDEMIOLOGIC STUDY TYPES COHORT STUDIES CASE-CONTROL STUDIES CROSS-SECTIONAL STUDIES

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.

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.

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

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)

THE MAIN DESCRIPTIVE STUDY IN EPIDEMIOLOGY: THE 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.

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

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.

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

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

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

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