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Measuring burden of disease

Measuring burden of disease. Introduction to DALYs FETP India. Objective of this lecture. Understand methods used to estimate burden of disease in terms of death and disability. Key areas. Cases Deaths Years of life lost (YLLs) Disability-adjusted life years (DALYs) Age weighting

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Measuring burden of disease

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  1. Measuring burden of disease Introduction to DALYs FETP India

  2. Objective of this lecture Understand methods used to estimate burden of disease in terms of death and disability

  3. Key areas • Cases • Deaths • Years of life lost (YLLs) • Disability-adjusted life years (DALYs) • Age weighting • Discounting

  4. Reasons to measure burden of disease • Assign priorities between different public health problems • Compare strategies that a single public health problem in terms of impact • Choose health interventions that target different health problems with different strategies Cases

  5. Cases • Allow comparing health interventions targeting the same problem • Do not allow • Comparisons between diseases • Does not take into account • Case fatality • Disability Cases

  6. Cases: Examples • Number of cases of malaria • Number of cases of tuberculosis • Number of HIV infections Cases

  7. Deaths • Allow comparing health interventions targeting the same problem • Allow comparing different diseases • Does not take into account • Age at death • Disability Deaths

  8. Deaths: Examples • Comparing the number of deaths from malaria with the number of deaths from tuberculosis • Estimating the number of deaths prevented through a sanitation programme Deaths

  9. Years of life lost (YLLs) • Allow comparing health interventions targeting the same problem • Allow comparing different diseases • Take into account age at death • Do not take into account • Disability YLLs

  10. Life expectancy Birth Early death Years of life lost Years of life lost Life expectancy Birth YLLs

  11. Years of life lost to present deaths (1/3) • Information required • Age at death • Sex • Country / region • Estimating life expectancy • Depends upon age, sex and region • Obtained in Global Burden of Disease life tables Years of life lost = Life expectancy - age at death YLLs

  12. Death today Life expectancy Years of life lost Years of life lost to present deaths (2/3) Survival today Life expectancy YLLs Life expectancy at the age of death

  13. Years of life lost to present deaths (3/3) • What is the number of years of life lost to AIDS in India in 2000? • Elements needed: • 2000 AIDS death rates (N) • Age distribution of death cases (Age) • Life expectancy (LE) at the age of death YLL =  N x (LE-Age) Age groups YLLs

  14. Years of life lost to future deaths (1/3) • Year by year cohort analysis • Estimate mortality secondary to other causes (years censored) • Estimate number of deaths that will occur because of the disease studied • Natural history • Calculate years of life lost through subtracting age at death to life expectancy YLLs

  15. Year 1 Year 2 Year 3 Death from other causes Years of life lost Death from other causes Years of life lost Death from other causes Years of life lost Years of life lost to future deaths (2/3) Year 0 Life expectancy YLLs

  16. Years of life lost to future deaths (3/3) • What will be the number of years of life lost between 2000 and 2030 because of HIV infections acquired in India in 2000? • Elements needed: • HIV infections in India in 2000 • Age distribution of cases of infection • Background mortality by age • AIDS specific death rate, year by year after infection YLLs

  17. Disability-adjusted life years (DALYs) • Allow comparing health interventions targeting the same problem • Allow comparing different diseases • Take into account age at death • Take into account disability DALYs

  18. The concept of disability • Life in a state of perfect health is lived to its full potential • Life in case of disease is lived lived partially • Disability weight DALYs

  19. 4 years lived 75% 2 years lived 100%, 2 years lived 50% 3 years lived 100%, 1 year lived 0% Measuring death and disability with the same metric Year 0 Year 1 Year 2 Year 3 Life expectancy 4 years lived 100% DALYs

  20. Disability-adjusted life years (DALYs) • Summary measure • Take into account loss due to • Death (Years of life lost, YLLs) • Disability (Years lived with disability, YLDs) • The equivalence is: • Death = 100% disability • Perfect health = 0% disability DALYs

  21. 4 years lived 75% (Disability weight [DW]: 25%): One DALY lost 2 years lived 100%, 2 years lived 50% (DW: 50%): One DALY lost 3 years lived 100%, 1 year lived 0%: One DALY lost The equivalence between disability and death Year 0 Year 1 Year 2 Year 3 Life expectancy 4 years lived 100%: No DALY lost DALYs Total: 3 DALY lost

  22. Calculating DALYs • Calculate years of life lost through death • Calculate years of life lived with disability • Add the two Year 0 Year 1 Year 2 Year 3 1 year lived 100%, 2 years lived 50%, 1 year lost: 2 DALYs lost DALYs

  23. DALYs lost to present conditions (1/3) • Estimate years lived with disability (YLDs): • Estimate the prevalence of the disease (e.g., viral hepatitis B) • Estimate the prevalence of the sequalae of the disease • Hepatocellular carcinoma (Specific disability weight) • Decompensated cirrhosis (Specific disability weight) • Chronic active hepatitis (Specific disability weight) • Multiply number affected by the disability weights • Estimate years of life lost (YLLs) because of death: • Specific mortality • Calculate YLLs using life expectancy • Add YLDs and YLLs DALYs

  24. DALYs lost to present conditions (2/3) Year of the study One year, 30% disability weight Life expectancy One year, 50% disability weight One year, 70% disability weight DALYs Years of life lost Total: 2.5 DALYs lost

  25. Calculating DALYs lost in the future • Year by year cohort analysis • Background mortality to estimate mortality secondary to other causes (years censored) • Estimate YLLs because of death • Natural history to estimate specific mortality • Calculate YLLs using life expectancy • Estimate YLDs • Natural history to estimate morbidity and duration secondary to the disease • Multiply years at disability status by disability weight • Add YLDs and YLLs DALYs

  26. Calculating DALYs lost in the future Year 0 Year 1 Year 2 Year 3 Life expectancy Death from other causes Years of life lost Death from other causes Years of life lost Death from other causes Years of life lost DALYs

  27. The Global Burden of Disease Study • Goes against disease-specific approaches • Integrates all causes of death and disability • Uses death certificates as starting point • The “mortality envelope” • Assigns deaths to • Immediate causes • Risk factor to health • Uses DALYs as the universal metric to compare public health issues DALYs

  28. Age weights • One year lost does not have the same meaning according to the age • Age weights attribute lower weights for • Childhood • Older age Age weights

  29. Discounting • DALYs do not have the same value if lost • Today (e.g., measles) • Later (e.g., hepatitis B) • Discounting rate • Rate that discounts the value each year • Apply to costs and effects • E.g., 3% • Subject to discussion • Should DALYs be discounted? • At what rate? Discounting

  30. Comparison between various measures of burden

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