Measuring health status using the Health Utilities Index

Abstract

The aim of this study was to evaluate interrater and intermodality agreement in assessing health status using the Health Utilities Index. A random sample from a Dutch cohort of 14-year-old Very Low Birth Weight children and their parents were invited to participate in a face-to-face (n = 150) or telephone (n = 150) interview. All 300 participants were also sent a questionnaire by mail. Response rate was 68%. Interrater and intermodality agreement were high for the physical HUI3 attributes and poor for the psychological attributes. Children and parents reported more dysfunction in the psychological attributes when interviewed than when completing the mailed questionnaire. High agreement on the physical attributes may have resulted from the fact that hardly any dysfunction was reported in these attributes, and poor agreement in the psychological attributes may have been a result of the fact that in these attributes much more dysfunction was reported. In measuring children's health status using the HUI3, the results and their interpretation vary with the source of information and the modality of administration. For maximum comparability between studies, written self-report questionnaires seem the preferred option.

Introduction

In medicine, the effects of prevention and therapy are conventionally measured in terms of mortality and morbidity. In chronic diseases, however, mortality and morbidity show little variance and the patient's priorities may lie elsewhere. In evaluation studies in chronic conditions, health status and health-related quality of life are therefore important additional measures of outcome. For these measures, it is claimed that patients themselves are the preferred respondents. This claim rests on two assumptions: first, that the crucial concept to be measured is the patient's own perception of health, and second, that the patient is the best observer and reporter of this perception 1, 2. Self-reports may, however, be difficult or impossible to obtain, for instance in the severely ill or cognitively impaired. It may then be necessary to invite a spouse, a doctor or a nurse to report on the patient's behalf. The validity of using these so-called proxies as respondents in health surveys has been the subject of several studies, most of which show only partial agreement between proxy report and self-report. In measuring children's health status, parents are commonly used as proxy respondents. This strategy is clearly needed with very young children, who cannot act as respondents. Even in school children and adolescents, the use of parents as valid proxy informants has been advocated 3, 4, despite the fact that at this age children are generally capable of communicating their perception of health. Existing evidence suggests that, as in adult patients, agreement between proxy report and self-report depends on the observability of the domain 5, 6, 7. It has also been found that proxies consistently report less dysfunction in psychological domains than do children themselves 8, 9, 10.

A second important issue in assessing health status is the way the information is obtained. Options include mailed questionnaire, face-to-face interview or telephone interview. It has been argued that the anonymity of a mailed questionnaire invites respondents to be more candid [11], but empirical studies addressing this issue have thus far shown conflicting results 12, 13, 14, 15, 16.

If studies differ with respect to source of information and modality of administration, the resulting sets of data relating to health status cannot be directly compared. In the present study, we analyzed interrater and intermodality agreement on the Health Utilities Index Mark 3 (HUI3) [17]. This was done in the context of an international multicenter study investigating outcomes of very low birth weight or small for gestational age infants. As the participating centers did not apply identical modalities of administration, or use identical sources of information, this analysis is required to interpret intercountry differences in health results, should they exist. The aim of this analysis was: (1) to determine intermodality agreement comparing mailed questionnaires with telephone interviews and with face-to-face interviews from parents and children, respectively; and (2) to determine interrater agreement between parents and children, taking modality into account.