HSBH1012 · Introduction to Health and Health Care
Patterns of Health & Disease
Week 2 of University of Sydney HSBH1012 describes the health of whole populations: the burden of disease and its core metric, the DALY = YLL + YLD, alongside life expectancy, mortality and morbidity, and the Global Burden of Disease study's leading causes. One DALY represents the loss of one year of full health, which lets diseases that kill early be compared with diseases that disable without killing. Week 2 is examined in the open-book Early Feedback quiz, and its reading (on the “worth” of a disease) joins the reflection-exam pool.
What this chapter covers
- 01Burden of disease (AIHW): quantifying the gap between living to old age in good health and life shortened by illness, injury, disability and early death
- 02DALY = YLL + YLD — the core metric; one DALY = loss of one year of full health; YLL = years of life lost to premature mortality, YLD = weighted years lived with disability
- 03The Global Burden of Disease (GBD) study: mortality and disability across countries, time, age and sex
- 04Life expectancy (years a person can expect to live at a given age, if current death rates hold) and healthy life expectancy / HALE
- 05Mortality (deaths ÷ population) vs morbidity (disease and disability); crude, age-specific and cause-specific death rates
- 06Global life-expectancy-at-birth time series: 28.5 (1800) → 67 (end of 20th C) → 72 (2016) → 73.4 (2023)
- 07Leading global causes of death/DALYs (2019): ischaemic heart disease, stroke, COPD, lower respiratory infections, neonatal conditions …
- 08The epidemiological shift toward non-communicable diseases (NCDs) and away from communicable, maternal, neonatal & nutritional (CMNN) causes
Applied: computing and interpreting a DALY
- +2(a) State the formula as taught: DALY = YLL + YLD. Substitute: DALY = 100 + 60 = 160 DALYs. (Units are years of healthy life lost.)
- +1(b) One DALY represents the loss of the equivalent of one year of full (healthy) life — so 160 DALYs means 160 years of full health lost to this condition in the population.
- +1(c) Drowning causes premature death but little lived disability — its burden is almost all YLL. Cataract-blindness causes disability but rarely death — its burden is almost all YLD.
- +1(c cont.) Because the DALY adds both onto one common scale (years of full health lost), the two very different conditions can be placed side by side and prioritised for resource allocation — the reason burden of disease is measured at all.
Key terms
- Burden of disease
- A way of quantifying the gap between the ideal of living to old age in good health and the reality of life shortened by illness, injury, disability and early death (AIHW). Measures both fatal and non-fatal impact.
- DALY
- Disability-Adjusted Life Year. DALY = YLL + YLD; one DALY represents the loss of one year of full health. The core burden-of-disease metric.
- YLL (years of life lost)
- The years of life lost due to premature mortality — the fatal component of the DALY.
- YLD (years lived with disability)
- The weighted years lived in less-than-full health due to disease or injury — the non-fatal component of the DALY.
- Life expectancy
- The number of years a person can expect to live at a given age (e.g. at birth), assuming current death rates do not change. HALE adds a quality adjustment for years lived in less-than-full health.
- Mortality vs morbidity
- Mortality = the number of deaths relative to the population (crude, age-specific or cause-specific rates); morbidity = the presence of disease and disability in a population.
Patterns of Health & Disease FAQ
What is the DALY and how is it calculated?
The DALY (Disability-Adjusted Life Year) is the core burden-of-disease metric, taught as DALY = YLL + YLD: years of life lost to premature mortality plus the weighted years lived with disability. One DALY represents the loss of one year of full health. It is powerful because it puts fatal and non-fatal impact on one scale, so a condition that kills early (drowning) can be compared with one that disables without killing (cataract blindness).
What is the difference between the DALY and YLL?
YLL (years of life lost) captures only premature mortality — the years lost because people die younger than a reference life expectancy. The DALY adds YLD (weighted years lived with disability) on top: DALY = YLL + YLD. So a disease with lots of disability but few deaths will have a DALY much larger than its YLL. Mixing them up is the classic Week 2 error.
Why do we measure burden of disease at all?
To compare unlike diseases on a common scale and to guide decisions. Measuring burden lets a country see its biggest contributors to lost healthy life, identify preventable risks, design interventions, and provide evidence for resource allocation and policy. In Australia, for example, dementia rose from the 12th to the 2nd leading cause of total burden between 2003 and 2023 — a shift that matters for where money and services go.
Can AI help me with burden-of-disease calculations?
Yes. Sia can walk you through DALY = YLL + YLD with fresh numbers, explain HALE versus life expectancy, quiz you on the leading global causes of death, and help you interpret a burden figure in words — which is what the exam actually asks. It explains step by step and checks your reasoning; it does not complete graded assessment for you. Confirm details on Canvas.
Exam move
Make DALY = YLL + YLD automatic, and always be able to say what each term means and why the sum is useful (comparing fatal and non-fatal conditions, guiding resource allocation) — the exam rewards interpretation over recall. Memorise a few high-yield anchor figures you can drop into a reflection: global life expectancy at birth reached 73.4 years in 2023, and Australia's burden splits roughly half fatal / half non-fatal. Practise the Week 2 take-home questions (define burden of disease; name key indicators; distinguish DALY from YLL) as short structured answers, then draft your Week 2 reflection on the essential reading. Ask Sia to generate a YLL/YLD scenario and check both your arithmetic and your one-sentence interpretation.
Working through Patterns of Health & Disease in HSBH1012? Sia is AskSia’s AI Health Sciences tutor — ask any HSBH1012 Patterns of Health & Disease question and get a clear, step-by-step explanation grounded in how HSBH1012 is taught and assessed. Read this chapter free, then take your hardest questions to Sia.
