Measures of epidemiology (mortality, infant mortality, morbidity, life expectancy) and their use in identifying priority health issues in Australia

Australia spends roughly $240 billion a year on health (around 10% of GDP). The decisions about where that money goes depend on epidemiological data: who is sick, with what, who is dying, and how many years of healthy life are being lost. This dot point covers the six core measures the syllabus expects you to know and the strengths and weaknesses of each.

What is epidemiology

Epidemiology is the study of patterns and causes of health and disease in populations. It does not study individuals; it studies groups. The job of an epidemiologist is to gather the data, look for patterns, and feed those patterns back to governments and health services so they can act. The Australian Institute of Health and Welfare (AIHW) is the main federal agency for this work; the Australian Bureau of Statistics (ABS) produces the underlying population and death data.

The six measures the syllabus expects

Mortality

Mortality is the death rate. It is usually expressed as deaths per 100,000 population per year. The ABS Causes of Death dataset is the canonical Australian source. Recent leading causes of death in Australia are ischaemic heart disease, dementia and Alzheimer disease, cerebrovascular disease (stroke), lung cancer, and chronic obstructive pulmonary disease (COPD).

Strengths. Hard data. Every death in Australia is registered. Comparable across years and across countries.

Weaknesses. Mortality only captures who dies, not who suffers. A chronic disease like depression has low direct mortality but enormous burden. Mortality misses non-fatal priorities.

Infant mortality

Infant mortality is deaths of children under 1 year of age per 1,000 live births. It is an extremely sensitive measure of overall population health, maternal health care quality, and socioeconomic conditions. Australia sits around 3 per 1,000 nationally (AIHW 2024). The Indigenous infant mortality rate is roughly double the non-Indigenous rate, which is itself a priority signal.

Strengths. A single number that captures the quality of an entire system of maternal and child health care.

Weaknesses. It tells you a population is doing well but not what specifically to fix.

Morbidity

Morbidity is illness and disease in a population. Two sub-measures matter:

• Incidence: the rate of new cases of a disease in a defined period (e.g., new cancer diagnoses per year).
• Prevalence: the proportion of a population with a condition at a point in time (e.g., 1 in 10 Australians have diabetes).

Morbidity catches conditions that do not kill quickly but do reduce quality of life. The AIHW Burden of Disease Study tracks morbidity for chronic conditions like mental disorders, musculoskeletal conditions, and asthma.

Strengths. Captures the experience of illness, not just death.

Weaknesses. Hard to measure precisely; relies on patients seeking treatment and being diagnosed. Under-reports conditions where stigma prevents seeking care (mental health, sexual health).

Life expectancy

Life expectancy at birth is the average number of years a person born today is expected to live, given current mortality rates. Australian life expectancy is around 83 years, among the highest in the world. The gap between Indigenous and non-Indigenous life expectancy is 7-8 years for males and 6-7 years for females (AIHW Closing the Gap report 2024).

Strengths. A single intuitive number that summarises population health. Excellent for between-group comparisons.

Weaknesses. Hides what people die of, and treats years lived in poor health the same as years lived in good health.

DALYs (Disability-Adjusted Life Years)

A DALY is one lost year of healthy life. It is the sum of:

• YLL (Years of Life Lost) from premature death, and
• YLD (Years Lived with Disability) from time in poor health.

So one DALY equals either one year of life lost or one year lived with a fully disabling condition. The AIHW Australian Burden of Disease Study uses DALYs to compare the total impact of conditions that kill (cancer, heart disease) against conditions that disable (mental disorders, musculoskeletal). Mental and substance use disorders rank in the top three burdens for Australians despite low direct mortality, because they cause enormous YLD.

Strengths. Combines fatal and non-fatal burden into one number, making cross-condition comparison possible.

Weaknesses. Disability weights are subjective. DALYs treat one year of severe back pain as a number, which can feel reductive.

HALE (Health-Adjusted Life Expectancy)

HALE is life expectancy adjusted for the time spent in poor health. Australian HALE is around 71 years, meaning the average Australian can expect roughly 12 years of life at the end where their health is significantly impaired. HALE is used to argue for prevention spending: extending life by reducing chronic disease in middle age increases HALE proportionally more than late-life treatment does.

How these measures identify priorities

A priority for Australia's health emerges when the data agrees across several measures. Cardiovascular disease ranks high on mortality, high on morbidity, and high on DALYs. That triangulation is what justifies it as a National Health Priority Area.

Mental health, by contrast, is invisible on mortality alone but enormous on morbidity and DALYs. Including DALYs and morbidity is what surfaced mental health as a National Health Priority Area in 1996 and kept it there.

The syllabus expects you to be able to argue from data to priority. In an extended response, name the measure, give the specific number with the source, and link it to the priority it identifies.