Summary measures of population health

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Summary measures of population health

• M Stud in Public Health
• 2002-3

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• Background

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The drive to quantification for policy purposes

• Key document
• World Bank, Investing in health, WDR, 1993
• Background
• Confounding of specialist knowledge and advocacy
• Schooling and health services as investment in
  human capital

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Central ideas

• Economic rationalisation
• Ie Using estimates of health benefit per spent
  as the main guide to public health policy
• Requires
• Robust summary measure of health
• Assumes
• Health mainly depends on resources purchaseable
  with money

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Dean Jamison

• Directed the production of Investing in health
• Ph.D., Economics, Harvard University, 1970
  Professor of Social Research MethodsJoint
  Appointment to School of Public HealthDirector,
  Center for Pacific Rim Studies2002-4 NIH
• Adviser to World Bank and WHO
• Areas of Interest (from UCLA www)
• Economics of educational reform in the United
  States economic aspects of health sector policy
  in developing countries and health and
  nutritional determinants of children's
  educational performance.

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Chris Murray

• D.Phil., 1988, Oxford University M.D., 1991,
  Harvard University Professor of International
  Health Economics
• Formerly, Director of Global Burden of Disease
  Unit, Center for Population and Development
  Studies, Harvard
• Director, Global Programme on Evidence for Health
  Policy, WHO Geneva
• Professor of Public Health, Oxford declined

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Global Burden of Disease, 1996-

• World Bank, WHO
• Theoretical basis for the WDR of 1993
• Estimates for all global regions of burden of
  disease in 1990
• Main measure DALY

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The Global Burden of Disease methodology

• Measures healthy time lost from both fatal and
  non-fatal conditions
• Units Disability Adjusted Life Years
• DALYs lost can be attributed to
• Contributing diseases and injuries
• Causes
• Draws on - demography
• - epidemiology
• - economics

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World Health Report 2000

• Used
• Disability Adjusted Life Expectancy (DALE)
• as summary measure of population health

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Rankings for attainment
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Rankings for performance
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Reactions?

• Sporadic apoplexy!
• Political and peer review processes
• Sudhir Anand chairs peer group
• Special web site
• http//www.who.int/health-systems-performance/docs
  /listofdebates.htm

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Summary measures of population health

• Are already playing a major role in international
  public health policy
• Exploring these measures from an epidemiological
  perspective will be a major theme of this module

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Summary measures of health Essence

• Combine information on mortality and non-fatal
  health states to measure levels of health in
  populations
• Intrinsically normative
• In construction and use

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Uses

• Comparing health levels in populations
• Comparing health levels in 1 population at
  different times
• Measuring inequalities
• Giving appropriate attention to non-fatal
  conditions
• Informing consideration of priorities

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Unidimensional or multidimensional?

• Money is unidimensional!
• So resource allocation decisions
• even where only implicit
• imply a single ranking

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Summary measures

• Need to be distinguished from their data inputs
• Instruments to measure health / disability levels
  in the living
• are normative
• Choices and value judgements are used in their
  construction and use

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Desirable attributes of summary measures of health

• Should be sensitive to all types of health loss
• cf measures using thresholds eg disability-free
  life expectancy
• Should only take account of age and sex
• not eg country of residence
• Should treat like health states as like
• Should use metric of time
• rather than event rates

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• Why metric of time?

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Deaths from stroke and RTAs comparisons on 2
measures, East Anglia 1990
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Deaths from stroke and RTAs comparisons on 2
measures, East Anglia 1990
Assuming all decedents would otherwise have
survived to 75
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Deaths from stroke and RTAs comparisons on 2
measures, East Anglia 1990
Assuming all decedents would otherwise have
survived to 75
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Occurrence measures in public health

• Studying causation
• Metric of incidence typically optimal
• Comparing health levels
• Metric of time typically optimal
• Ie time lived in specified health states

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Life tables yield average time lived
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Summarising time spent at different health levels

• Divides each lifetime into
• A part lived in full health (A)
• A part lived in less than full health (B)

C
B
A
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2 families of measures

• Health expectancies
• A f (B)
• Where full health 1
• Eg DALE
• Health gaps
• C g (B)
• Where 1 is equivalent to
  death
• Eg DALY

C
B
A
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Health expectancies

• Active life expectancy
• Disability-free life expectancy
• Disability-adjusted life expectancy (DALE)
• Years of healthy life
• Quality-adjusted life expectancy
• etc

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Attributes of health expectancies

• Period or cohort
• Calculation method
• Prevalence / double decrement / multi-state
• Definition and measurement of health
• Eg Active le lt- measures of ADL
• Methods used to value health states
• Incorporation of other values

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f (B)
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Measuring health levels in the living

• Controversial
• Subjective preferences (utilities)
• Consistent with economic authodoxy

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• Self-reported health can show marked regressive
  bias when used in comparisons between populations

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Life expectancy in India compared to the US, mid
1990s
Sen, BMJ 2002 324, 861
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Self-reported morbidity, India (mid-1970s) and US
(mid-1980s)
Sen, BMJ 2002 324, 861
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Measuring health levels in the living

• Controversial
• Subjective preferences (utilities)
• Consistent with economic authodoxy
• But, especially for group comparisons,
• Self reports subject to serious (regressive) bias

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Methods used to value health states

• Whose values
• Individuals in states / general public /
  professionals / household carers
• Type of valuation question
• Standard gamble / time trade-off / person
  trade-off / visual analogue
• How health states are presented
• Range of health states valued
• Valuation process ? deliberative

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Essence of health gaps (eg DALY)

• Amount of healthy life lost relative to some norm

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Attributes of health gaps (eg DALY)

• Implied target or norm
• Some vary with mortality level in population
• How health states defined measured
• ? Dimensions
• ? Self-perception vs observation
• Method used to value health states
• Inclusion of other values
• Eg Age-weighting, time-preference, equity weights

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Age structure dependence

• Health expectancies intrinsically age-independent
• Health gaps
• Age-dependent when expressed in absolute terms
• (DALYs lost in population X in year Y)
• But can be age-standardised

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Desirable properties of summary measures for
comparative uses

• Criteria for optimality of a measure should not
  be confused with criteria for resource allocation
• Murray et al use Rawlsian veil of ignorance
  approach to specify criteria

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Criteria for summary measures for comparative uses

• If, for a given cause/health state in any
  given age group, everything else being equal
• Mortality ? ? measure ?
• Measures using gaps relative to current
  population fail
• Prevalence ? ? measure ?
• Incidence-based measures fail
• Incidence ? ? measure ?
• Prevalence-based measures fail
• Remission ? ? measure ?
• Severity (within a given state)? ? measure ?

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Other desirable properties of health measures

• Comprehensibility and feasibility
• Eg life expectancy does well despite complexity
• Additive decomposition
• Ie Total contribution of (a b c)
• For eg disease groups or risk factors
• All health expectancy measures fail

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• Losses (gaps) can be attributed to diseases or to
  determinants
• health expectancies can not

C
B
A
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Calculating the contribution of diseases,
injuries and causes

• Only possible with Gap measures
• Methods
• Categorical
• Eg ICD rules TB with HIV is assigned to HIV
• But ?myocardial infarction in diabetic or liver
  cancer with chronic hep B
• Counterfactual
• Compare current or future with expected under
  specified alternative

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But health expectancies can be more readily
understood

• and so appeal to journalists and politicians
• DALE used in World Health Report 2000

C
B
A
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Health expectancies

• Active life expectancy
• Disability-free life expectancy
• Disability-adjusted life expectancy (DALE)
• Years of healthy life
• Quality-adjusted life expectancy
• etc

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Conclusions

• Some measures fail basic tests
• Eg those using internal mortality norms or
  simple dichotomies for less than perfect health
  (eg disability-free life expectancy)
• None simultaneously fulfil prevalence and
  incidence criteria
• Only gap measures (eg DALYs) permit
  decomposition by conditions and causes

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The marginalist critique (Williams et al)

• Summary measures (totals) not useful for policy
• What we need to know is the next best thing to do
  at the margin
• But
• why not use both totals and marginals?
• Totals also protect against partisan use of
  epidemiology (disease advocacy)

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Conclusion

• The DALY is in use
• Its derivation and characteristics need to be
  understood by public health professionals