![]() ![]() Socially desirable response - if study participants consistently give the answer that the investigator wants to hear, then information bias would occur.Missing data - if certain individuals consistently have missing data, then information bias would occur.Recall bias - if individuals can't remember exposures accurately, then information bias would occur.Misdiagnosis - if a diagnostic test is consistently inaccurate, then information bias would occur.Instrumentation - an inaccurately calibrated instrument creating a systematic error.Information bias (misclassification bias): Systematic error due to inaccurate measurement or classification of disease, exposure, or other variables. For example, suppose the study population includes multiple racial groups but members of one race participate less frequently in the type of study. In a cross-sectional study, the sample may have been non-representative of the general population.If the length of residence is related to the exposure then our sample is biased toward subjects with less exposure. For example, people who are mobile are more likely to change their residence and be lost to follow-up. In a cohort study, people who share similar characteristics may be lost to follow-up.If controls are selected among hospitalized patients, the relationship between an outcome and smoking may be underestimated because of the increased prevalence of smoking in the control population. Exposure may affect the selection of controls – e.g, hospitalized patients are more likely to have been smokers than the general population.Ascertaining a case based upon previous exposure creates a bias that cannot be removed once the sample is selected. ![]() Only those taking the medication were assessed for the problem. If a press release encourages people taking this pain reliever to report to a clinic to be checked to determine if they are a case and these people then become the cases for the study, a bias has been created in sample selection. Suppose a new outbreak is related to a particular exposure, for example, a particular pain reliever. Some investigators may identify cases predicated upon previous exposure.If a study only recruits cases among patients receiving medical care, there will be selection bias. Persons who are treated by a physician are far more likely to be diagnosed (and identified as cases) than persons who are not treated by a physician. Many older people have experienced this injury to some degree, but have never been treated for it. Suppose you are selecting cases of rotator cuff tears (a shoulder injury). ![]()
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