Interdisciplinary Research on Healthy Aging:Introduction

Background: This is an introduction to a Special Collection of Demographic Research on Interdisciplinary Research on Healthy Aging. The collection is an outcome of an international conference in China on biodemography and multistate modeling in healthy aging research. Causal analysis is the common theme of the papers. Healthy aging is an outcome of pathways of causally related distant and proximate determinants and intervening factors that mediate the effects of the determinants. Objective: The objective is to introduce the papers in this SC and to highlight the place of multistate modeling in causal analysis. Methods: We adopt the common distinction between structural causal modeling and dynamic causal modeling. The papers in the SC concentrate on structural causal modeling. Multistate models (and, more particularly, the continuous-time Markov process model) are oriented more toward dynamic causal modeling. In dynamic causal modeling the causal dependencies are defined in terms of events (outcomes), exposure time, and transition rates that relate exposures to events. Results: The contributions to the SC illustrate the progress made in structural causal modeling in the study of healthy aging. Dynamic causal analysis, however, has progressed comparatively slowly. Contribution: The papers in the SC and the brief introduction to multistate modeling in causal analysis pave the way to enhanced causal analysis in the study of healthy aging and in demography

Comparative empirical evaluations of internal migration models in subnational population projections

While population forecasters place considerable emphasis on the selection of appropriate migration assumptions, surprisingly little attention has been given to the effects on projection outcomes of the way internal migration is handled within population projection models. This paper compares population projections for Australia's states and territories prepared using ten different internal migration models but with identical assumptions for fertility, mortality and international migration and with the internal migration model parameters held constant. It is shown that the choice of migration model generates large differences in total population, geographical distribution and age--sex composition. It is argued that model choice should be guided by balancing model reality with practical utility and model performance is examined against these criteria. Of the ten models evaluated the authors argue that the migration pool, biregional, and biregional with net constraints models offer a good compromise between conceptual rigour and practicality. If the projected origin-destination flows are required then one of the versions of the standard multiregional model with reduced data inputs is preferred. The large variation in projection outputs points to the need for a better understanding of the spatio-temporal structure of migration in Australia

Global, regional, and national burden of disorders affecting the nervous system, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

Background: Disorders affecting the nervous system are diverse and include neurodevelopmental disorders, late-life neurodegeneration, and newly emergent conditions, such as cognitive impairment following COVID-19. Previous publications from the Global Burden of Disease, Injuries, and Risk Factor Study estimated the burden of 15 neurological conditions in 2015 and 2016, but these analyses did not include neurodevelopmental disorders, as defined by the International Classification of Diseases (ICD)-11, or a subset of cases of congenital, neonatal, and infectious conditions that cause neurological damage. Here, we estimate nervous system health loss caused by 37 unique conditions and their associated risk factors globally, regionally, and nationally from 1990 to 2021. Methods: We estimated mortality, prevalence, years lived with disability (YLDs), years of life lost (YLLs), and disability-adjusted life-years (DALYs), with corresponding 95% uncertainty intervals (UIs), by age and sex in 204 countries and territories, from 1990 to 2021. We included morbidity and deaths due to neurological conditions, for which health loss is directly due to damage to the CNS or peripheral nervous system. We also isolated neurological health loss from conditions for which nervous system morbidity is a consequence, but not the primary feature, including a subset of congenital conditions (ie, chromosomal anomalies and congenital birth defects), neonatal conditions (ie, jaundice, preterm birth, and sepsis), infectious diseases (ie, COVID-19, cystic echinococcosis, malaria, syphilis, and Zika virus disease), and diabetic neuropathy. By conducting a sequela-level analysis of the health outcomes for these conditions, only cases where nervous system damage occurred were included, and YLDs were recalculated to isolate the non-fatal burden directly attributable to nervous system health loss. A comorbidity correction was used to calculate total prevalence of all conditions that affect the nervous system combined. Findings: Globally, the 37 conditions affecting the nervous system were collectively ranked as the leading group cause of DALYs in 2021 (443 million, 95% UI 378–521), affecting 3·40 billion (3·20–3·62) individuals (43·1%, 40·5–45·9 of the global population); global DALY counts attributed to these conditions increased by 18·2% (8·7–26·7) between 1990 and 2021. Age-standardised rates of deaths per 100 000 people attributed to these conditions decreased from 1990 to 2021 by 33·6% (27·6–38·8), and age-standardised rates of DALYs attributed to these conditions decreased by 27·0% (21·5–32·4). Age-standardised prevalence was almost stable, with a change of 1·5% (0·7–2·4). The ten conditions with the highest age-standardised DALYs in 2021 were stroke, neonatal encephalopathy, migraine, Alzheimer's disease and other dementias, diabetic neuropathy, meningitis, epilepsy, neurological complications due to preterm birth, autism spectrum disorder, and nervous system cancer. Interpretation: As the leading cause of overall disease burden in the world, with increasing global DALY counts, effective prevention, treatment, and rehabilitation strategies for disorders affecting the nervous system are needed. Funding: Bill & Melinda Gates Foundation