Summary Measures of Population Health: Measuring the impact

of disease, injuries and risk factors

ObjectivesObjectives• To derive internally consistent estimates of

incidence, prevalence, disease progression and mortality for over 100 disease and injury categories– Communicable, maternal, perinatal and nutritional conditions– Non-communicable diseases– Injuries

• To elicit a numerical value (weight) reflecting the general population’s relative preference for each disease/disability state on an interval scale

Summary Measures of Summary Measures of Population Health (SMPH)Population Health (SMPH)

• Expectancy - life years lived– Health Adjusted Life Expectancy (HALE)– Disability Adjusted Life Expectancy (DALE)– Disability Free Life Expectancy (DFLE)

• Gap - life years lost (compared to ideal)– Disability Adjusted Life Year (DALY)– Health Adjusted Life Years Lost (HALY)

Calculating HALYsCalculating HALYsHALY = YERF + YLLHALY = YERF + YLL

“Full Health” “Partial Health” “Premature mortality”

Years of Life Lost due to premature mortality

(YLL)

Year Equivalents of life lost due to Reduced Functioning

(YERF) +

Disease (Stage and Severity)

BirthDeath

Potential limits

to life

= Health Adjusted Life Years lost

Calculating YLLCalculating YLL

Death Life Expectancy

Years of life lost to premature mortality

YLL = M * L

where M = number of deathsL = remaining life expectancy

Calculating YERFsCalculating YERFs

Disease Death

Years of life lived with the disease

YERF = I * (1-P) * D

where I = incident casesP = preference scoreD = average duration

model

Key inputs to summary measuresKey inputs to summary measures

• Mortality by age, sex and cause

• Epidemiological data on non-fatal health outcomes by age, sex and cause

• Valuations of health states

Top 10 Leading Causes of Death Top 10 Leading Causes of Death and DALYs and DALYs (data from Canada)(data from Canada)

Leading cause of death 1 Ischaemic heart disease 2 Stroke 3 Lung Cancer 4 COPD 5 Colorectal cancer 6 Dementia 7 Diabetes mellitus 8 Prostate Cancer 9 Breast Cancer 10 Suicide

DALYs 1 Ischaemic heart disease 2 Stroke 3 COPD 4 Depression 5 Lung cancer 6 Dementia 7 Diabetes mellitus 8 Colorectal cancer 9 Asthma 10 Osteoarthritis

-4 -2 0 2 4 6 8 10 12

Unsafe sex

Occupation

Illicit drugs

High blood cholesterol

Lack of fruit/veg.

Obesity

Alcohol benefit

Alcohol harm

High blood pressure

Physical inactivity

Tobacco

Attributable DALYs as a proportion of total DALYs

YLL

YLD

Burden attributable to Burden attributable to 10 risk factors10 risk factors

HALYHALYTotal for top 15 cancersTotal for top 15 cancers

0 50 100 150 200 250

Liver cancerEsophageal cancer

Bladder cancerKidney cancer

Ovarian cancerStomach cancer

Brain cancerLeukemia

Pancreatic cancerNon-Hodgkin's lymphoma

Prostate cancerAll other cancers

Breast cancerColorectal cancer

Lung cancer

Thousands

YLL

YERF

Attribution of total HALYS for all Attribution of total HALYS for all cancers combined to Risk Factorscancers combined to Risk Factors

0 5 10 15 20 25 30

Alcohol

Obesity

Physical Inactivity

Fruit and Vegetables

Tobacco (1991)

Tobacco (direct)

Tobacco (indirect)

Percent

Total = 49%

Part 2: Weighting of Health Part 2: Weighting of Health StatesStates

• To elicit a numerical value (preference score) on an interval scale reflecting the population’s relative preference for health states

• Describe health in terms of functional status or capacity

Eliciting Health State PreferencesEliciting Health State Preferences

Methods Tested:

• Visual Analog Scale (VAS)

• Standard Gamble (SG)

• Time Trade Off (TTO)

• Person Trade Off (PTO)

Visual Analog ScaleVisual Analog Scale

1

0

0.5

0.75

0.25

Death

Full Health

Poor Health

Standard GambleStandard Gamble

Give instantaneous and lasting improvement to full health with probability p

Give immediate death with probability 1-p

You have a lifelong stationary impaired health state and are given a choice. Do you take a hypothetical procedure that will:

Time Trade-OffTime Trade-Off

• Years of healthy life you would give up to avoid living in a state of poor health

Person Trade Off (PTO)Person Trade Off (PTO)

1,000 healthy individuals

N 1,000 individuals in a disabling health state