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

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E l ti V lid Evaluating Valid 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 Bi 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 ideological perspective 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 l h t h d th ti h 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: 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: 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 Exposed and unexposed Cases and controls Types of Bias Design phase: 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: Non-response bias: (type of selection bias) Observation bias Attrition bias (retrospective/prospective cohort studies) Diagnostic suspicion bias Information bias (recall, interviewer) Exposure/outcome misclassification (measurement bias) T f Bi ( t’d) Types of Bias (cont’d) Analysis Data dredging, circle the significant findings C f di bi (U i 8) d i / l i Confounding bias (Unit 8): design/analysis Interpretation Inadeq ate re ie of the literat re Inadequate review of the literature Publication bias Note: Other biases exist beyond those we will discuss http://dorakmt.tripod.com/epi/bc.html Who is responsible?
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