Global burden of 288 causes of death and life expectancy decomposition in 204 countries and territories and 811 subnational locations, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

BACKGROUND Regular, detailed reporting on population health by underlying cause of death is fundamental for public health decision making. Cause-specific estimates of mortality and the subsequent effects on life expectancy worldwide are valuable metrics to gauge progress in reducing mortality rates. These estimates are particularly important following large-scale mortality spikes, such as the COVID-19 pandemic. When systematically analysed, mortality rates and life expectancy allow comparisons of the consequences of causes of death globally and over time, providing a nuanced understanding of the effect of these causes on global populations. METHODS The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 cause-of-death analysis estimated mortality and years of life lost (YLLs) from 288 causes of death by age-sex-location-year in 204 countries and territories and 811 subnational locations for each year from 1990 until 2021. The analysis used 56 604 data sources, including data from vital registration and verbal autopsy as well as surveys, censuses, surveillance systems, and cancer registries, among others. As with previous GBD rounds, cause-specific death rates for most causes were estimated using the Cause of Death Ensemble model-a modelling tool developed for GBD to assess the out-of-sample predictive validity of different statistical models and covariate permutations and combine those results to produce cause-specific mortality estimates-with alternative strategies adapted to model causes with insufficient data, substantial changes in reporting over the study period, or unusual epidemiology. YLLs were computed as the product of the number of deaths for each cause-age-sex-location-year and the standard life expectancy at each age. As part of the modelling process, uncertainty intervals (UIs) were generated using the 2·5th and 97·5th percentiles from a 1000-draw distribution for each metric. We decomposed life expectancy by cause of death, location, and year to show cause-specific effects on life expectancy from 1990 to 2021. We also used the coefficient of variation and the fraction of population affected by 90% of deaths to highlight concentrations of mortality. Findings are reported in counts and age-standardised rates. Methodological improvements for cause-of-death estimates in GBD 2021 include the expansion of under-5-years age group to include four new age groups, enhanced methods to account for stochastic variation of sparse data, and the inclusion of COVID-19 and other pandemic-related mortality-which includes excess mortality associated with the pandemic, excluding COVID-19, lower respiratory infections, measles, malaria, and pertussis. For this analysis, 199 new country-years of vital registration cause-of-death data, 5 country-years of surveillance data, 21 country-years of verbal autopsy data, and 94 country-years of other data types were added to those used in previous GBD rounds. FINDINGS The leading causes of age-standardised deaths globally were the same in 2019 as they were in 1990; in descending order, these were, ischaemic heart disease, stroke, chronic obstructive pulmonary disease, and lower respiratory infections. In 2021, however, COVID-19 replaced stroke as the second-leading age-standardised cause of death, with 94·0 deaths (95% UI 89·2-100·0) per 100 000 population. The COVID-19 pandemic shifted the rankings of the leading five causes, lowering stroke to the third-leading and chronic obstructive pulmonary disease to the fourth-leading position. In 2021, the highest age-standardised death rates from COVID-19 occurred in sub-Saharan Africa (271·0 deaths [250·1-290·7] per 100 000 population) and Latin America and the Caribbean (195·4 deaths [182·1-211·4] per 100 000 population). The lowest age-standardised death rates from COVID-19 were in the high-income super-region (48·1 deaths [47·4-48·8] per 100 000 population) and southeast Asia, east Asia, and Oceania (23·2 deaths [16·3-37·2] per 100 000 population). Globally, life expectancy steadily improved between 1990 and 2019 for 18 of the 22 investigated causes. Decomposition of global and regional life expectancy showed the positive effect that reductions in deaths from enteric infections, lower respiratory infections, stroke, and neonatal deaths, among others have contributed to improved survival over the study period. However, a net reduction of 1·6 years occurred in global life expectancy between 2019 and 2021, primarily due to increased death rates from COVID-19 and other pandemic-related mortality. Life expectancy was highly variable between super-regions over the study period, with southeast Asia, east Asia, and Oceania gaining 8·3 years (6·7-9·9) overall, while having the smallest reduction in life expectancy due to COVID-19 (0·4 years). The largest reduction in life expectancy due to COVID-19 occurred in Latin America and the Caribbean (3·6 years). Additionally, 53 of the 288 causes of death were highly concentrated in locations with less than 50% of the global population as of 2021, and these causes of death became progressively more concentrated since 1990, when only 44 causes showed this pattern. The concentration phenomenon is discussed heuristically with respect to enteric and lower respiratory infections, malaria, HIV/AIDS, neonatal disorders, tuberculosis, and measles. INTERPRETATION Long-standing gains in life expectancy and reductions in many of the leading causes of death have been disrupted by the COVID-19 pandemic, the adverse effects of which were spread unevenly among populations. Despite the pandemic, there has been continued progress in combatting several notable causes of death, leading to improved global life expectancy over the study period. Each of the seven GBD super-regions showed an overall improvement from 1990 and 2021, obscuring the negative effect in the years of the pandemic. Additionally, our findings regarding regional variation in causes of death driving increases in life expectancy hold clear policy utility. Analyses of shifting mortality trends reveal that several causes, once widespread globally, are now increasingly concentrated geographically. These changes in mortality concentration, alongside further investigation of changing risks, interventions, and relevant policy, present an important opportunity to deepen our understanding of mortality-reduction strategies. Examining patterns in mortality concentration might reveal areas where successful public health interventions have been implemented. Translating these successes to locations where certain causes of death remain entrenched can inform policies that work to improve life expectancy for people everywhere. FUNDING Bill & Melinda Gates Foundation

Peer assisted learning in undergraduate clinical medical education: a mixed methods study

Peer-assisted learning (PAL) involves students learning with and from each other. PAL activities may be informal, or undertaken formally in a curriculum, with or without educator facilitation. Reports on PAL in medical education suggest its value can extend beyond technical knowledge gain, to development of broader professional skills. However, the literature largely focuses on the value of PAL in the university environment, rather than how it occurs in the clinical context. Medical students at Monash University are required to engage in PAL in their pre-clinical years. The researcher’s experience as learner and teacher suggested students also formulated PAL strategies for clinical placements. However, activities were not formalised and unlikely to be optimised. This research aimed to identify students’ and educators’ use and perceptions of PAL during clinical placements to develop recommendations for PAL in clinical settings. A tri-phasic study was designed using Biggs’ Constructive Alignment as a framework to characterise students’ PAL experiences, examining the intended, enacted, and perceived curriculum. Year 3 was the focus of the study, as this first clinical year contains many unstructured learning opportunities which may afford PAL. Research methods comprised a curriculum map (Phase 1), student survey and an observational study of the students on their clinical placements (Phase 2), and interviews with experienced educators (Phase 3). Whilst the curriculum map identified few explicit learning objectives relating to PAL, students reported participation in PAL activities during clinical placements on average 20 times per week. Observations supported this reported frequency of peer interactions: two-thirds of students’ time was spent in the company of peers. Survey and interview data revealed students valued teaching and feedback from peers, but doubted the accuracy of peer-generated information. The roles of ‘feedback giver’ and ‘observer’ were less valued by students. Significantly more female students reported that PAL contributed to a safe learning environment than males. PAL activities were reported to contribute to students’ evaluative judgement: the comprehension of and ability to judge performance against notions of quality. Educator involvement was perceived to be a key ingredient for successful PAL. These data were used to develop a PAL Activity Matrix, which identified activities students could partake in within a clinical environment to optimise their learning. In Phase 3, expert educators reported the study findings resonated with their own broader experience of PAL in clinical education. The activity matrix was confirmed as representing ideal strategies. Potential barriers and facilitators to the uptake of PAL were illuminated. These ‘real world’ considerations for culture, epistemic authority, and patient-centred care were included in the resultant implementation framework for PAL. This comprehensive study informs the current discourse on PAL in clinical medical education. It identifies barriers and facilitators to PAL, and presents strategies to improve the value of PAL. Future work could test the effect of PAL strategies on students’ clinical capacity, including technical competency, professional and communication skills, and preparedness and ability to teach. The use of PAL could also be examined in a broader range of clinical environments, at both undergraduate and postgraduate levels

Peer assisted learning in undergraduate clinical medical education: a mixed methods study

Peer-assisted learning (PAL) involves students learning with and from each other. PAL activities may be informal, or undertaken formally in a curriculum, with or without educator facilitation. Reports on PAL in medical education suggest its value can extend beyond technical knowledge gain, to development of broader professional skills. However, the literature largely focuses on the value of PAL in the university environment, rather than how it occurs in the clinical context. Medical students at Monash University are required to engage in PAL in their pre-clinical years. The researcher’s experience as learner and teacher suggested students also formulated PAL strategies for clinical placements. However, activities were not formalised and unlikely to be optimised. This research aimed to identify students’ and educators’ use and perceptions of PAL during clinical placements to develop recommendations for PAL in clinical settings. A tri-phasic study was designed using Biggs’ Constructive Alignment as a framework to characterise students’ PAL experiences, examining the intended, enacted, and perceived curriculum. Year 3 was the focus of the study, as this first clinical year contains many unstructured learning opportunities which may afford PAL. Research methods comprised a curriculum map (Phase 1), student survey and an observational study of the students on their clinical placements (Phase 2), and interviews with experienced educators (Phase 3). Whilst the curriculum map identified few explicit learning objectives relating to PAL, students reported participation in PAL activities during clinical placements on average 20 times per week. Observations supported this reported frequency of peer interactions: two-thirds of students’ time was spent in the company of peers. Survey and interview data revealed students valued teaching and feedback from peers, but doubted the accuracy of peer-generated information. The roles of ‘feedback giver’ and ‘observer’ were less valued by students. Significantly more female students reported that PAL contributed to a safe learning environment than males. PAL activities were reported to contribute to students’ evaluative judgement: the comprehension of and ability to judge performance against notions of quality. Educator involvement was perceived to be a key ingredient for successful PAL. These data were used to develop a PAL Activity Matrix, which identified activities students could partake in within a clinical environment to optimise their learning. In Phase 3, expert educators reported the study findings resonated with their own broader experience of PAL in clinical education. The activity matrix was confirmed as representing ideal strategies. Potential barriers and facilitators to the uptake of PAL were illuminated. These ‘real world’ considerations for culture, epistemic authority, and patient-centred care were included in the resultant implementation framework for PAL. This comprehensive study informs the current discourse on PAL in clinical medical education. It identifies barriers and facilitators to PAL, and presents strategies to improve the value of PAL. Future work could test the effect of PAL strategies on students’ clinical capacity, including technical competency, professional and communication skills, and preparedness and ability to teach. The use of PAL could also be examined in a broader range of clinical environments, at both undergraduate and postgraduate levels