Disentangling rectangularization and life span extension with the moving rectangle method

Focus on disability-free life expectancy: implications for health-related quality of life

BACKGROUND

Since the end of the industrial revolution, advances in public health and clinical medicine have contributed to dramatic decreases in infant and childhood mortality, improvements in health-related quality of life (HRQoL), increases in overall life expectancy (LE), and rectangularization of survival curves.

OBJECTIVES

In this article, we focus on disability that has occurred with the overall lengthening of LE in many populations and the implications this has for decreased HRQoL.

METHODS

We utilize the concept of rectangularization of population survival to depict the rising prevalence of disability associated with increased LE, especially among racial and ethnic minorities and people of low socioeconomic status (SES) and relate this to HRQoL.

RESULTS

Disability-free life expectancy (DFLE) and healthy life expectancy (HLE) are defined in terms of HRQoL. Specific attention is focused on disability experienced by disparate populations around the globe. By focusing on disparities in DFLE, and the need to expand LE to include HLE as a central component of HRQoL, this work provides an important counterpoint to the attention that has been paid to LE disparities according to race, gender, ethnicity, education, and SES.

DISCUSSION

By calling attention to those factors that appear to be the most important drivers of the differences in quality and length of DFLE between different groups (i.e., the components of the social gradient, exposure to chronic stress, systemic inflammation, and the psychological and biological mechanisms associated with the gut-brain axis) and, by logical extension, HRQoL, we hope to promote research in this arena with the ultimate goal of improving DFLE, HLE, and overall HRQoL, especially in disparate populations around the globe.

Rectangularization of the survival curve reconsidered: The maximum inner rectangle approach

Rectangularization of the survival curve-a key analytical framework in mortality research-relies on assumptions that have become partially obsolete in high-income countries due to mortality reductions among the oldest old. We propose refining the concept to adjust for recent and potential future mortality changes. Our framework, the 'maximum inner rectangle approach' (MIRA) considers two types of rectangularization. Outer rectangularization captures progress in mean lifespan relative to progress in maximum lifespan. Inner rectangularization captures progress in lifespan equality relative to progress in mean lifespan. Empirical applications show that both processes have generally increased since 1850. However, inner rectangularization has displayed country-specific patterns since the onset of sustained old-age mortality declines. Results from separating premature and old-age mortality, using the MIRA, suggest there has been a switch from reducing premature deaths to extending the premature age range; a shift potentially signalling a looming limit to the share of premature deaths.