Health inequalities in New Zealand: an examination of mortality and hospital utilisation trends, with reference to the compression of morbidity hypothesis

Abstract

This thesis examines health inequalities by area-level socioeconomic deprivation, and health in later life in New Zealand. It identifies whether expansion or compression of morbidity is occurring at the end of life. It asks if overall morbidity at a population level is likely to increase or decrease in future as life expectancy increases, and if the same trend is seen for more and less deprived areas. The focus of this research is the identification and dissemination of mortality and morbidity patterns present in two large datasets, using powerful but relatively simple techniques. Large administrative datasets on morbidity and public hospital discharges in New Zealand between 1974 and 2006 are used in the analyses.

The thesis consists of three papers. Each paper uses the same datasets, but addresses separate research questions using different methods. The first paper is an exploratory analysis of age-specific and age-standardised mortality and hospital bed day rates, which are used as a proxy for morbidity. The second paper explores lifetime morbidity by using period-prevalence life table functions including Hospital Utilisation Expectancies: a variation of health expectancies. The third paper uses individual record linkage between the mortality and hospital datasets to examine hospital use in the last few months of life.

Hospital bed day and mortality rates declined over the time period, and convergence was seen between more and less deprived areas. Individuals at the oldest ages (80 years and over) saw little variation in hospital or mortality rates by area deprivation. Strong evidence for compression of morbidity was observed, particularly at older ages. This was in the absence of evidence for rectangularisation of the survival curve, considered by some to be a prerequisite for compression of morbidity. Rectangularisation of the survival curve would be denoted by life expectancy increases slowing, indicating the nearing of a limit to life expectancy. Instead, compression of morbidity was achieved through a decline in the severity of morbidity in the months prior to death. No evidence of a change in the point at onset of morbidity prior to death was observed. There was however some evidence that the decline in hospital utilisation prior to death (particularly for deaths
at older ages) may be partly artefactual. Further research using a different measure of morbidity is required to either support or disprove this theory.

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Identifiers

ORCID for Ann Berrington: orcid.org/0000-0002-1683-6668

ORCID for Zoë Matthews: orcid.org/0000-0003-1533-6618

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