It is probable that physician have a higher index of suspicion for tuberculosis in children without BCG scar that those with BCG scar. If this is so and an association is found between Tuberculosis and not having BCG scar, the association may be due to-
Ans. is 'b' i.e., Interviewer bias Information (Observer or misclassification bias) o Information bias is a type of connitive bias o Are when propoion of subjects misclassified on exposure or disease. o Information bias occurs due to people's curiosity and confusion of goals when trying to choose a course of action. o 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. Coming back to question o Interviewer bias occurs because the investigator knows beforehand, the paicular procedure or therapy to which the patient has been subjected. o This prior information may lead him to focus more on the group which he knows, is more susceptible. o In the question the physician already knows that children without BCG scar (nonimmunized) children are more prone to develop Tuberculosis than patients with BCG scar (immunized) children. o This prior information will lead him to investigate children without BCG scar more thoroughly as he knows, that being unimmunized these children are more prone to develop T.B. o On the other hand while investigating children with BCG scar, the interviewer will be bit careless as he knows that these children are already immunized. o This will automatically lead to detection of more cases of T.B. in children without B.C.G. scar.
Selection bias
Interviewer bias
Surveillance bias
Non-response bias