3.5.1 information bias

3.5.1 information bias

1. 1 Information bias Information bias Bias resulting from flawed definition of study variables or measurement of study variables Results in erroneous classification of subjects with regard to exposure and/or outcome – this is called misclassification

2. 2 Information bias There are two types of misclassification: Non-differential misclassification Differential misclassification Definitions of these terms depend on the variable being measured (i.e., exposure or outcome)

3. Information bias Types of misclassification of outcome variables – Non-differential misclassification of outcome The degree of outcome misclassification is not related to exposure status Differential misclassification of outcome The degree of outcome misclassification depends on the exposure status – this is a more serious problem 3

4. Information bias Types of misclassification of exposure variables – Non-differential misclassification of exposure The degree of exposure misclassification is not related to outcome status Differential misclassification of exposure The degree of exposure misclassification varies by outcome status – this is a more serious problem 4

5. Information bias Some specific exposure related information biases – Recall bias: occurs when participants are asked about past exposure after the outcome in question has occurred (or not), as often happens in case- control studies 5

6. 6 Information bias The respondents’ memories vary according to whether or not they experienced the outcome, especially if the exposure is a commonly known risk factor for the disease they have experienced Those with disease and the exposure more likely to recall exposure Increased sensitivity Those with disease and not exposed more likely to report exposure Reduced specificity Will explain use of sensitivity and specificity to quantify information bias shortly

7. Information bias Some specific exposure related information biases – Recall bias example: Case-control study of gestational pesticide exposure and offspring developmental delay 50

8. 8 Information bias Recall bias example (cont.): Mothers with developmentally delayed children may more comprehensively recall their exposures during pregnancy or may over-report them, having spent time thinking about what might have caused their child’s disability Control mothers with typically developing children have not spent time pondering prenatal exposures, and thus may be less likely recall exposure

9. Information bias Some specific exposure related information biases – Interviewer bias: occurs when interviewers are not blinded to participant disease status 9

10. Information bias Interviewer bias: Interviewers may question diseased and non- diseased differently, for example emphasizing some words or questions, or asking more clarifying questions of those with disease in an attempt to elicit information on the exposure 10

11. 11 Information bias Some specific outcome related information biases Observer bias: occurs when observers/raters are not blinded to exposure status (analogous to interviewer bias, except affects disease classification) Observers/raters may be more likely to count cases among participants with high risk/exposure profiles

12. Information bias Some specific outcome related information biases – Observer bias example: A sample of nephrologists were sent patient case histories with a simulated race randomly assigned to each case When the case history identified the patient as black, the nephrologists were twice as likely to diagnose the patient as hypertensive end-stage renal disease, as compared to patients labeled white 12

13. Information bias Some specific outcome related information biases – Respondent bias: participants with high risk/exposure profiles may be more likely to report the outcome of interest 13

14. 14 Information bias Effects of non-differential versus differential misclassification In practice, it is impossible to correctly measure/collect all variables: some misclassification is inevitable Thus, it is important to thoroughly evaluate your exposure and outcome definitions, study protocol, and data collection procedures to evaluate what likely measurement error exists Then, think about the extent and direction of bias

15. 15 Information bias Non-differential misclassification Results in a bias toward the null when the exposure or disease that is misclassified is binary For example, when a binary exposure is measured with equal amount of error between case and control groups, it washes out the exposure-outcome association This is a conservative bias, and the investigator at least knows that she/he is not presenting an artificially large association

16. 16 Information bias Non-differential misclassification when there are more than two categories of the exposure or disease does not necessarily result in bias towards the null Categorization of a variable that has non-differential misclassification can generate differential misclassification

17. 60 Information bias Differential misclassification of exposure or disease results in a bias in an unpredictable direction – it may be toward the null or away from the null It is possible to evaluate the bias on a case-by-case basis and speculate the direction of the bias, however the possibility of bias away from the null is problematic Generally considered a more serious problem than bias towards the null because (a) the investigator does not know the direction of the bias with certainty, and (b) if the bias is away from the null, the investigator risks presenting an artificially inflated effect estimate vs. an attenuated one

18. 18 Information bias Misclassification of a confounding variable – Bias in an unpredictable direction

19. Information bias Numerical example of non-differential misclassification 19

20. 20 Information bias Measures useful for quantifying information bias Sensitivity P(classified positive|true positive) Specificity P(classified negative|true negative)

21. Information bias Case-control study data – the true distribution of exposure OR=? 21

22. Information bias 22 Se:P(class. positive|true positive), Sp: P(class. negative|true negative)

23. Information bias 23 Se:P(class. positive|true positive), Sp: P(class. negative|true negative)

24. Information bias True positive (exposed) cases = TP Classified positive (exposed) – = TPx(class pos|TP) – = 80 x 0.9 Classified negative (unexposed) – = TPx(1-(class pos|TP)) – = TPx(class neg|TP) – = 80 x 0.1 – Or = TP-class. positive 24 Se:P(class. positive|true positive), Sp: P(class. negative|true negative)

25. Information bias True negative (unexposed) cases = TN Classified positive (exposed) – = TNx(1-(class neg|TN)) – = TNx(class pos|TN) – = 20 x 0.2 – Or = TN-class. negative Classified negative (unexposed) – = TNx(class neg|TN) – = 20 x 0.8 25 Se:P(class. positive|true positive), Sp: P(class. negative|true negative)

26. Information bias 26 Se:P(class. positive|true positive), Sp: P(class. negative|true negative)

27. Information bias 27

28. Information bias 28

29. Information bias 29

30. 30 Information bias Non-differential because sensitivity and specificity the same for cases and controls Resulted in bias towards the null True OR = 4 Misclassified OR = 2.6

31. Information bias Numerical example of differential misclassification 31

32. Information bias Case-control study data – the true distribution of exposure OR=4 32

33. Information bias 33 Se:P(class. positive|true positive), Sp: P(class. negative|true negative)

34. Information bias 34 Se:P(class. positive|true positive), Sp: P(class. negative|true negative)

35. Information bias 35 Se:P(class. positive|true positive), Sp: P(class. negative|true negative)

36. Information bias 36 Se:P(class. positive|true positive), Sp: P(class. negative|true negative)

37. Information bias 80 Se:P(class. positive|true positive), Sp: P(class. negative|true negative)

38. 38 Information bias Differential because sensitivity and specificity NOT the same for cases and controls This example resulted in bias away from the null True OR = 4 Misclassified OR = 5.7 Can result in bias in either direction Exhibit 4-6 in Szklo – differential misclassification resulting in bias towards the null

39. 39 Information bias Information biases types summary Non-differential misclassification of exposure Sensitivity and specificity of exposure assessment not both 1.0 but the same for diseased and non-diseased Differential misclassification of exposure Recall bias Interviewer bias Sensitivity and/or specificity of exposure assessment NOT the same for diseased and non-diseased

40. 40 Information bias Information biases types summary Non-differential misclassification of outcome Sensitivity and specificity not both 1.0 but the same for exposed and unexposed Differential misclassification of outcome Observer bias Respondent bias Sensitivity and/or specificity NOT the same for exposed and unexposed