Population health and inequalities in health : measurement of health-related quality of life and changes in QALYs over time in Sweden

Abstract

People live longer, but all years are not in full health. A health policy which aims to improve both the average level of health and reduce inequalities in health needs a global measure which can be monitored over time. A summary measure of population health ideally should combine quantity (survival) and quality (health status or health-related quality of life (HRQoL)) into a single measure. Such a measure, quality-adjusted life years (QALYs), has been developed in the field of economic evaluation of health care. Estimation of QALYs requires data on survival and the corresponding health state score reflecting HRQoL on a scale between 0 (dead) and I (full health).

The overall aim of this thesis was to estimate HRQoL and QALYs on a population level and by socioeconomic group over time in Sweden, and to contribute to the methodology regarding summary measures of population health. This thesis also addresses the importance of whose preferences to use when valuing health states. The thesis is based on five papers.

Two data sources were used to obtain health states scores. Study I and II were based on the 1998 Stockholm County Public Health Survey where the generic HRQoL measure, the EQ-5D self-classifier (where respondents may classify their health into five dimensions within three levels of severity), and a rating scale and a time trade-off (TTO) question were included. Study III-V were based on the Statistics Sweden's Survey of Living Conditions (ULF). Responses to selected survey questions in the ULF were mapped into the EQ-5D, using the UK EQ-5D tariff to derive health state scores.

Survival data over time were obtained from the official Swedish mortality statistics. To estimate mortality rates by socio- economic group, data from the ULF survey linked to the National Cause of Death Register were used. The health state scores were combined with the calculated life-table survival probabilities to estimate QALYs.

In the Stockholm Public Health Survey, most problems were reported in the dimension pain/discomfort, followed by the dimension anxiety/depression, and the prevalence of problems increased with age (Paper I). However, in the dimension anxiety/depression, next to the oldest age group most problems were reported in the youngest age group. Women had lower health state scores than men. After controlling for age, sex, and disease, the HRQoL was lower in the manual than in the non- manual groups. The Stockholm study also suggests that individual and social TTO values differ systematically and that the difference increases with severity (Paper II). Study III-V support the feasibility of obtaining mean health state scores by mapping survey data to the EQ-5D in order to obtain health state scores for time periods where no HRQoL data were available (Paper III).

Life expectancy for newborn males (females) increased by 3.68 (2.70) years from 1980/81 to 1996/97 (Paper IV). Expected QALYs increased by 2.64 (0.54). Older persons experienced considerable health gains over time whereas the health gains were small or nonexistent for younger women. For 20-year-old men (women) the difference in life expectancy between the highest and the lowest socio-economic group was 2.11 (1.56) years in 1980 and 3.79 (2.15) years in 1997 (Paper V). Corresponding differences in QALYs were 5.76 (4.14) in 1980 and 7.06 (5.66) in 1997, indicating an increase in inequalities in life expectancy and QALYs over time. However, the widening socio-economic inequalities were more stable for men than for women.

This thesis provides an example of methods of obtaining health state scores from existing survey data, and of combining survival and HRQoL into a summary measure of health, QALYs, to explore the population health and inequalities in health over time.