09-SelectionBias

09-SelectionBias - Principles of Epidemiology for Public...

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3/15/2011 Sources of error: Selection bias 1 Sources of error: Selection bias Victor J. Schoenbach, PhD Department of Epidemiology Gillings School of Global Public Health University of North Carolina at Chapel Hill www.unc.edu/epid600/ Principles of Epidemiology for Public Health (EPID600)
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2 Excerpts from (allegedly) actual student history essays collected by teachers from 8th grade through college Richard Lederer, St. Paul's School http://www.edfac.usyd.edu.au/staff/souters/Humour/Student.Blooper.World.html
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3 Excerpts from (allegedly) actual student history essays collected by teachers from 8th grade through college Richard Lederer, St. Paul's School “Finally Magna Carta provided that no man should be hanged twice for the same offense.” “Another story was William Tell, who shot an arrow through an apple while standing on his son's head.”
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4 Excerpts from (allegedly) actual student history essays collected by teachers from 8th grade through college Richard Lederer, St. Paul's School “It was an age of great inventions and discoveries. Gutenberg invented removable type and the Bible. Another important invention was the circulation of blood. Sir Walter Raleigh is a historical figure because he invented cigarettes and started smoking. And Sir Francis Drake circumcised the world with a 100 foot clipper.”
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5 Winning tongue in cheek headlines selected for humorous magazine cover contest (Epimonitor.net) “Don’t Ask, Don’t Tell---Double Blinding In Military Studies” (Melissa Adams) Sensitivity Analysis---Are You Really A New Man? (Mark Colvin) Absent Sex Life? Lucky You! 38 Sexually Transmitted Diseases You Won’t Get (Mark Colvin) Do You Have Survey Phobia? Take Our Quiz and Find Out!! (Mary Anne Pietrusiak)
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3/15/2011 Sources of error: Selection bias 6 “To error is human” Science emphasizes systematic, repeatable, carefully-conducted observation Laboratory investigations are highly controlled, to minimize unwanted influences Human sciences must contend with many threats to validity www.cfa.harvard.edu/poem/
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10/29/2001 Sources of error: Selection bias 7 “To error is human” Any epidemiologic study presents many, many opportunities for error in relation to: Selection of study participants Classification and measurement Comparison and interpretation
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3/15/2011 Sources of error: Selection bias 8 Accuracy, Bias, Error, Precision, Reliability, Validity Accuracy : lack of error – getting the correct result Bias : systematic error – independent of study size Error : discrepancy between the observed result and the true value Precision : absence of random error Reliability : repeatability of a measure Validity : absence of bias (or absence of all error)
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09-SelectionBias - Principles of Epidemiology for Public...

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