Use of surrogate respondents in studies of stroke and dementia

A study was performed to determine the misclassification of information on exposure when surrogate informants are interviewed. Information from nondementia patients admitted to a geriatric ward was compared with that obtained from the patients' family members or friends (informants). Thirty-seven patients were recruited (17 with current or previous stroke, and 20 no history of stroke). Information on past medical and family history, cigarette smoking and alcohol consumption was collected using a questionnaire that was administered independently to patients and informants. For nonstroke patients, agreement on smoking and alcohol consumption at different ages was generally good. Informants reported slightly lower smoking and alcohol intake than patients: 1.3 fewer total pack-years (95% CI, -3.8, +6.5) and 2.7 fewer units/week (95% CI, -1.5, +6.9), respectively. For stroke patients, informants tended to report a greater smoking consumption at all ages, and a slightly higher alcohol consumption. Informants reported an excess of 7.4 total pack-years (95% CI, -1.2, + 16.0) and 2.19 units/week (95% CI, -1.0, +5.3). Agreement for medical history was good, except for hypertension. There was poor agreement for family medical history. The impact of misclassification is discussed.