Study was conducted to see for role of radiation in leukemia, 100 patients selected among which 70 given history of exposure, among 100 controls 30 giving history of exposure. What is the bias in the study ?
Correct Answer: Recall bias
Description: Ans. is 'b' i.e., Recall bias Information (Observer or misclassification bias) Information bias is a type of connitive bias Are when propoion of subjects misclassified on exposure or disease. Information bias occurs due to people's curiosity and confusion of goals when trying to choose a course of action. It may be of following types i) Repoing bias Individual with severe disease tends to have complete records therefore more complete information about exposures and greater association found. ii) Recall bias (memory bias) Those who have disease (cases) have a greater sensitivity for recalling exposure than those who dont have disease (controls). iii) Interviewer bias Caused by the action of the interviewer, e.g., Interviewer generally devote more time to cases as compared to controls. iv) Hawthorne bias (Attention bias) It is caused by change in behavior of human subjects of an experiment, simply becasue they know that they are being observed. For example, if we want to study the smoking as a risk factor for lung carcinoma and we take 2 groups (50 smokers and 50 nonsmoker) and follow them for 10 years. It may be possible that over the time study subjects may change their behavior, e.g. 5 out of 50 smokers quit smoking behavior. This will cause Hawthorne bias. It is quite obvious that Hawthorne effect will occur in prospective studies (where the study subject are being observed), e.g. in Coho Study. This bias will not occur in retrospective study as the study subjects are not observed rather their history is taken.
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