Lecture 12b - Categories of Epidemiologic Studies...

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Categories of Epidemiologic Studies Epidemiologic Studies Observational Experimental Descriptive Analytic (Case reports) (Case series) Prospective cohort Retrospective cohort Case-control Randomized controlled trials Community trials Ecologic Cross-sectional
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Descriptive Observational Studies Most commonly used to look for patterns of disease Measure occurrence of disease and/or risk factors for disease (exposures) in a population Answer the questions: Who? What? Where? When? May suggest a direction to explore Why?, but cannot provide an answer due to lack of an explicit comparison group
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Analytic Observational Studies In contrast to descriptive studies, analytic studies incorporate a formal comparison group Test specific etiologic hypotheses or Generate new hypotheses or Suggest mechanisms of causation As knowledge about likely etiologic factors builds, preventive hypotheses can be tested
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The Epidemiologic Study Uncontrolled Assignment Controlled Assignment EXPERIMENTAL STUDIES OBSERVATIONAL STUDIES Sampling with regard to disease/outcome Sampling with regard to exposure Randomized person assignment Community assignment CASE- CONTROL STUDIES COHORT STUDIES RANDOMIZED CONTROLLED TRIALS COMMUNITY TRIALS
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Cumulative Incidence Number of new cases of disease during a time period Number of subjects followed for the time period “The only way to interpret risk is to know the length of the time period over which the risk applies” Cumulative Incidence = Risk or Probability
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Person-Time Incidence Rate Deals with uneven follow-up time by only considering time at risk contributed by each person in the study Person time: i.e. 100 person years = 100 persons x 1 year or 50 persons x 2 years or 25 persons x 4 years, etc…. Rate base: 100, 1000, 100,000 person-years In published incidence rates, often the person-years are implied. Example: cancer risk of 8.5 per 100,000 Number of new events in a specified time period Total person time at risk x Rate Base
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Point Prevalence Rate (point prevalence proportion)
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This note was uploaded on 02/23/2012 for the course EPID 301 taught by Professor Richardson&aronson during the Spring '09 term at Queens University.

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Lecture 12b - Categories of Epidemiologic Studies...

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