Survey into health problems of elderly people: multivariate analysis of concordance between self-report and proxy information.

<bold>Background: </bold>In many cases probands are unable to give information about their own history. Our objective was to compare information given by elderly people on their past and current health and family history of illness with similar information given by a relative, friend or carer.<bold>Material: </bold>In three urban and two rural areas of England and Wales a sub-sample, weighted by age and cognitive status, was drawn from random population samples of people aged >/=65, not permanently living in hospital, and interviewed between 1991 and 1994, plus for each of these a relative, friend or carer.<bold>Methods: </bold>The relation between the reports of probands and informants on cognitive function, lifetime illnesses, current health problems, and family history of illness was analysed using multiple regression of agreement, measured using Cohen's kappa, and logistic regression of bias and of proportion of 'not known' responses. Potential explanatory variables used were: centre, proband cognitive function, proband sex, informant sex, proband age, difference in age (generation), relationship, frequency of contact, period known, modality of informant interview.<bold>Results: </bold>Overall agreement per interview measured by kappa between informant and proband was lower for older probands, probands who were cognitively impaired, and those who saw one another less often; each effect adjusted for all the others using multiple regression. Informants tended to over-report relative to probands if the proband was cognitively impaired, male, they themselves were female, of a younger generation, and co-resident; each effect adjusted for all the others using logistic regression. Interviews were more likely to be missing at least one item if the informant was not the spouse, had known the proband for less time, and was not co-resident; each effect adjusted for all the others using logistic regression.<bold>Conclusion: </bold>There is reasonable accord between probands and informants which is enhanced by close contact, long period of knowledge, and a female informant. Degree of kinship is not critical. Informant interviews may be conducted by telephone rather than face-to-face without serious loss of quality. [ABSTRACT FROM AUTHOR]