Mechanisms for Nondifferential Misclassification
Nondifferential misclassification can occur in a number of ways. Records may be incomplete, e.g., a medical record in which none of the healthcare workers remember to ask about tobacco use. There may be errors in recording or interpreting information in records, or there may be errors in assigning codes to disease diagnoses by clerical workers who are unfamiliar with a patient's hospital course, diagnosis, and treatment. Subjects completing questionnaires or being interviewed may have difficulty in remembering past exposures. Note that if difficulty in remembering past exposures occurs to the same extent in both groups being compared, then there is nondifferential misclassification, which will bias toward the null. However, if one outcome group in a case-control study remembers better than the other, then there is a differential misclassification which is called "recall bias." Recall bias is described below under differential misclassification of exposure.
Mechanisms for Nondifferential MisclassificationNondifferential misclassification can occur in a number of ways. Records may be incomplete, e.g., a medical record in which none of the healthcare workers remember to ask about tobacco use. There may be errors in recording or interpreting information in records, or there may be errors in assigning codes to disease diagnoses by clerical workers who are unfamiliar with a patient's hospital course, diagnosis, and treatment. Subjects completing questionnaires or being interviewed may have difficulty in remembering past exposures. Note that if difficulty in remembering past exposures occurs to the same extent in both groups being compared, then there is nondifferential misclassification, which will bias toward the null. However, if one outcome group in a case-control study remembers better than the other, then there is a differential misclassification which is called "recall bias." Recall bias is described below under differential misclassification of exposure.
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