Farid Najafi MD PhD School of Population Health Kermanshah University of Medical Sciences Rational and objectives How is it possible to compare the overall health status of a population with another population ID: 277994
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Slide1
Summary of measures of population Health
Farid
Najafi
MD PhD
School of Population Health
Kermanshah University of Medical SciencesSlide2
Rational and objectives
How is it possible to compare the overall health status of a population with another population
Objectives
Calculation of life expectancy
Interpretation of health expectancies
Interpretation of health gaps
Social value choices made in constructing summary measures of population healthSlide3Slide4
Additional readingSlide5
Importance of indicators
Importance of a comprehensive health indicator
Infant and maternal mortality?
Such indicators should be simple (preferably a single number) with an intuitive interpretationSlide6
Life expectancy
Life expectancy at birth is a widely used indicator
Summarises
the detailed current age-specific mortality into a single number
Calculated life expectancy is an underestimate of the actual number of years a newborn may expect to live
WHO annually publishes life expectancy per country (www.who.int/whr/en/)Slide7Slide8Slide9
Interpretation
Improvement over time
Most gains were made at birth rather than at age 30 or age 65
Reflection of prevention of childhood infections due to improvements in housing, nutrition and other
socio-economic circumstancesSlide10
Life table
Life expectancy is calculated using life table
It describes what would happen to a hypothetical group of 100000 newborn infants if they would experience the same mortality rate at each age as are recorded currently in the population of interest.Slide11Slide12Slide13
Definition of items in life table
I
x
= Life table cohort. A cohort to follow for dying of all of them
L
x
= years of lived=I
x+1
+d
x
/2
T
x
=Cumulative years lived
T
97
=T
98+
T
99+
T
100
e
x=life expectancySlide14
More interpretation on life table
life expectancy as an age-weighted mortality indicator
Value of preventing death at different age
Preventing death at age 0 save 76 years
Preventing death at age 98 save 2.55 yearsSlide15
Years of life lost
Potential years of life lost (PYLL): developed in 1940s to describe mortality due to tuberculosis
Advantages:
Easy to calculate
Younger age death counts for more
Can be calculated for specific cause
Disadvantage:
Arbitrary cut of point
Exclusion of some deathsSlide16
PYLL
First a cut-off must be chosen: the age below which deaths are considered ‘premature’
Often a cut-off of 65 or 70 is chosen
Summing all the differences over all deathsSlide17
Expected years of life lost (EYLL)
The number of life years lost by a death is equal to the life expectancy at that age
Death at younger ages count for more
EYLL can be calculated for specific diseases
Problem of equity:
Comparing two ethnic group with their life table?Slide18
Gaps and expectancies
Health expectancies
Life expectancy
Not possible to subdivide life expectancy into separate disease-specific expectancies
Cause-elimination life table
Health Gaps
Years of life lost
PYLL and EYLL
Population size matters for the gaps but not for the expectancies: years of life lost for large population is larger than for a small populationSlide19
Adding morbiditySlide20
Adding morbidity
The simplest way to combine mortality and morbidity into a single health expectancy is to calculate disability free life expectancy (DFLE)
It needs normal life table plus age-specific data on disability prevalence from a survey
It involves adjusting the number of years lived by survivors in each age group by the probability that those years are lived with a disability
Disadvantages
Disability score
It ignores years lived with disability- equality of years lost by death and years lived with disabilitySlide21
Quality adjusted life year (QALY)
The concept developed as an outcome measure in clinical trial
Here the benefit is defined as a better survival, a better health-related quality of life, or any combination of the two
Benefit of hip replacement
Basic idea: a life year lived in perfect health gets a health related quality of 1, and a year not lived (dead) gets a quality of 0. All health states between perfect health and death get a value between 1 and 0.Slide22
Example
5 years lived, of which 3 in perfect health (quality=1), 1.5 with mild pain (quality=0.8) and 0.5 with sever pain (quality=0.4) amounts to 4.4 QALYsSlide23
Disability adjusted life years (DALYs)
Developed by Christopher Murray and Alan Lopez for global burden of disease
Is a health gap indicatorSlide24
Issues
How long should people in good health expect to live?
Are all people equal? Do all people lose the same amount of health through death at a given age, even if there are variations in current life expectancies between population groups?
Use of a standard life table with life expectancy at birth of 82.5 in women with a lower standard for men (80 years)Slide25
Issues
How should we compare years of life lost through death with years lived with poor health or disability of various levels of severity?
Years lived with disability (YLD) for each disease is calculated using disease incidence, duration of disease, and a severity adjustment using a disability weight (DW)
Severity scales between 0 (being perfect health) and 1 ( being the worst possible health state (equated to being dead)Slide26
Issues
Is a year of healthy life gained now worth more to society than a year of healthy life gained sometime in future, for instance in 20 years’ time?
A 3% time discount rate is applied to future health loss to estimate the net present value of years of life lost.
A year of healthy life gained in 10 years’ time is worth 26% less than one gained now Slide27Slide28
Issues
Are lost years of healthy live valued more at some ages than others?
GBD weighted a year of healthy live lived at young ages and older ages lower than for other agesSlide29Slide30Slide31