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22 Cards in this Set
- Front
- Back
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What is bias?
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Systematic deviation of results or inferences from the truth
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What are the problems with bias?
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create spurious association
mask a true association |
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When does bias occur?
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in all study types and designs
usually do to investigator or study participants |
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When can bias be fixed?
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cannot be fixed, should be minimized in the design phase but analysis cannot get rid of bias
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What is random error?
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equal misclassification of cases and controls, will even out in a large enough sample
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Which type of error leads to imprecise results? Which type leads to inaccurate results?
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imprecise = chance (random error)
inaccurate= bias (systematic error) |
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What are the major types of bias?
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selection
information confounding |
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What is selection bias?
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animals are not representative of the population
(selection is not independent of exposure or outcome) |
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What is self-selection bias?
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people choose to enroll their animals, and may have sicker or healthier animals than the rest of the population
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What is response bias?
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usually seen with questionnaires, where the responders are more willing to fill out the survey because it is close to them or something like that
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What is loss to followup bias?
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animals lost to follow-up are different than the study population as a whole
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How can you minimize selection bias?
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clearly define the study population
explicitly ID case and control definitions Take cases and controls from the same population |
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What is information bias?
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The method of gathering information is inappropriate and leads to systematic error in measurement of the exposure or outcome
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What are examples of information bias?
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recall bias
reporting bias interview bias |
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What is recall bias?
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Exposed subjects have a greater sensitivity of recall
ie owner looking for ways to explain the animal's condition etc |
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What is reporting bias?
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reports of information are more detailed and complete for sicker animals, may be able to find greater association
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What is interview bias?
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The interviewer has a systematic bias in soliciting, recording and interpreting information (especially problematic if exposure or outcome status is already known)
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How can you minimize information bias?
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blinding
questionnaires with multiple questions asking the same information increased accuracy by double checking records and gathering data from multiple sources use multiple controls |
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What is a confounder?
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a factor related to both exposure and outcome which accounts for some or all of the relationship between the two
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Why is confounding an issue?
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describes a true association, but may be misleading as to the causation
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What are common confounders?
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age, species, sex
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How can you deal with confounding?
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randomization and matching of participants
restriction of potential confounders use stratified or multivariable analysis *better to try and reduce problems during study design rather than analysis |
