Study Design2

Analytical study design advantage & disadvantage

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objectives Define study design Describe type of analytical studies List advantage and disadvantage of each.

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Study designs Def: a specific plan or protocol for conducting the study, w allows the investigator to translate the conceptual hypothesis into an operational hypothesis.

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Analytical studies Analyzing relationship between variables

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Cross –sectional studies The data is collected on the study subjects at a specific point in time Advantage: Feasible, relatively easy Less time consuming Less costly Allow study several dis and exposure at the same time Useful for health planning ١٤٣٠/١٢/١١

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Cross –sectional studies Disadvantage Temporal ambiguity Do not know how long the cases had the dis Not suitable for study rare dis

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Case-control studies Individuals diagnosed as having a case are compared e individuals who do not have it

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Design of a case-control study

exposed

Cases People e dis

Not exposed

population

exposed

Controls People e/o dis

Not exposed

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Case-control studies Advantages: Least expensive Least time consuming Suitable for study of rare dis Disadvantages: Not suitable for rare exposures Cannot calculate frequency measures Liable to selection bias Liable to control bias ١٤٣٠/١٢/١١

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Cohort studies A gp of people who are free of outcome are classified by exposure ( control & experimental) followed for the development of outcome

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Design of a cohort study

dis No dis

exposed People e/o dis

dis

population

Not exposed No dis

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Cohort studies Advantages: No temporal ambiguity Selection of subjects cannot bias exposure estimation Several outcomes for each exposure could be studied, during F.U

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Cohort studies Disadvantages: Expensive Time-consuming Inefficient for rare dis Loss of FU

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