unit 7 pt 1 - Unit 7 Overview Overview Evaluating Valid...

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Evaluating Valid Statistical Associations Statistical Associations: Bias – Part 1 Part 1 Dr Borenstein Dr. Borenstein NO AUDIO ON THIS SLIDE. CLICK NEXT TO CONTINUE >> Unit 7 Overview ± Definition of bias ± Common types of biases ± Selection bias in cohort and case-control studies ± Observational/information biases: surveillance Observational/information biases: surveillance, recall, interviewer, item non-response ± Most important biases in cohort studies ± Most important biases in case-control/cross- sectional studies ± Biases in analytic phases of a study ± Misclassification: Differential and non- differential and their effects on the RR/OR ± Ways to avoid bias Unit 7: Evaluating Valid Statistical Unit 7: Evaluating Valid Statistical Associations ± Chance ± Bias ± Confounding Bias From Wikipedia, the free encyclopedia A bias is a prejudice in a general or specific sense, usually in the sense for having a preference to one particular point of view or ideologica perspective ideological perspective. Bias – example everyone can Bias example everyone can relate to… ± State of the Union speech 1/31/06 ± Poll taken of a sample of 464 people who watched the entire speech on TV ± Wolf Blitzer (CNN) says that the % Wolf Blitzer (CNN) says that the % approval ratings are not a reflection of the entire nation, only those who watched the entire speech. ± These people are special in that: ² They may be partisan and like Bush more than people who did not watch the speech How do we declare a “valid” (true) How do we declare a valid (true) statistical association? The problem of bias ± Definition of bias: ² The systematic error in the ± design ± conduct ± analysis ± dissemination/publication of a study that results in a mistaken estimate of an exposure’s effect on the risk of disease (Schlesselman 1982).
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Another way to think about Bias ± Making unfair (biased) comparisons between groups ² Exposed and unexposed ² Cases and controls Types of Bias ± Design phase: ² Selection bias ± Selection of cases and controls (case-control study, cross- sectional study) ± Selection of the unexposed cohort in historical (retrospective cohort studies (external comparison); rarely a problem in prospective cohort studies) ± Design/conduct: ² Non-response bias: (type of selection bias) ² Observation bias ± Attrition bias (retrospective/prospective cohort studies) ± Diagnostic suspicion bias ± Information bias (recall, interviewer) ± Exposure/outcome misclassification (measurement bias) Types of Bias (cont’d) ± Analysis ² Data dredging, circle the significant findings ² Confounding bias (Unit 8): design/analysis ± Interpretation Inadeq ate re ie of the literat re ² Inadequate review of the literature ² Publication bias ± Note Note: ² Other biases exist beyond those we will discuss ± http://dorakmt.tripod.com/epi/bc.html Who is responsible?
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This note was uploaded on 07/15/2011 for the course PHC 6000 taught by Professor Staff during the Summer '08 term at University of South Florida - Tampa.

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unit 7 pt 1 - Unit 7 Overview Overview Evaluating Valid...

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