DALY (Disability Adjusted Life Years)

Introduction:

DALY stands for Disability Adjusted Life Years.
From the name itself, DALY is the number of years of life adjusted/compromised by a person due to disease or disability
The concept of DALY was developed by Harvard University and it was commissioned by the World Bank
DALYs represent the total number of years lost due to illness, disability, or premature death
It is a mainly a measure for burden of disease
DALY can be considered/calculated as sum of: years of life lost (YLL) due to premature mortality and years lived with disability (YLD) due to the occurrence of disease
DALY is a metric which merges the burden of both morbidity and mortality into single number
It measures the amount of healthy life lost as a result of disability/premature death of a person
It is a measure of overall disease burden expressed as the collective number of years lost due to ill health, disability or early death
DALY takes both morbidity and mortality into account
This metric was initially used by World Health Organization (WHO) to assess global burden of disease
It is also used to measure the quantity and quality of life of the people in a combined form
1 DALY= 1 Healthy Life Year Lost OR 1 Lost year of Healthy Life
DALY combines two measures: YLL (Years of Life Lost due to premature mortality) and YLD (Years Lived with Disability due to disease morbidity)
Basic formula for DALY can be also understood as: YLL+YLD
YLL is further calculated as number of deaths (N) multiplied by standard life expectancy at the age at which death occurs (L) i.e. YLL= N*L (without applying social preferences like sex differences, disability weighting etc)
Similarly, in case of YLD, earlier, we used to consider the incidence of certain disease/cases while recently Global Burden of Disease (GBD) 2010 has started looking at prevalence of disease. Therefore, the new way to calculate YLD is number of prevalent cases (P) multiplied by disability weight (DW) i.e. YLD= P*DW (without applying social preferences)
The numerical interpretation of DALY is as such:
- If DALY= 0, its perfect health &
- If DALY=1, its worst possible health state/death
Averting one DALY means preventing 1 healthy life year from being lost. It may be preventing from either morbidity or mortality or both
DALY’s classification system has three groups in its system. They are:
- Group I: Communicable Diseases
- Group II: Non-Communicable Diseases
- Group III: Injuries

Uses/Advantages of DALY:

To measure the difference between current health status and ideal health status of the people
To assess and compare the impact of different diseases in a population. This will be further helpful to prioritize the interventions
To signify the total burden of disease in a country/region. This can be done by adding DALY from all the diseases
The effect of mortality and morbidity can be overviewed in a combined way, from a single measurement
It can be used to determine actual health research priorities for the country as DALY gives the information regarding fatal and non-fatal health outcomes

Limitations of DALY:

The concept of DALY is not widely used in other sectors outside health
The baseline measurement of DALY was done in developed countries. Thus, it may not reflect the difference in resources between the developed and developing countries
It is difficult to get the actual estimate of total number of people suffering from particular disease/pathogen in developing countries considering the poor effectiveness and efficiency of health system in these countries.

References:

http://www.who.int/healthinfo/global_burden_disease/metrics_daly/en/

http://www.givewell.org/research/DALY

http://www.psi.org/publication/what-is-a-daly/

http://www.who.int/mental_health/management/depression/daly/en/

http://www.physio-pedia.com/Disability-Adjusted_Life_Year

https://www.med.uottawa.ca/sim/data/DALY.htm

http://www.mf.uni-lj.si/dokumenti/6b695fc9385e3e2ab8fb41ec7d34660d.pdf

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3776440/

https://www.nimh.nih.gov/health/statistics/global/index.shtml

https://www.healthknowledge.org.uk/e-learning/health-information/population-health-specialists/lifetables-hales-dalys-pylls

http://documents.worldbank.org/curated/en/482351468764408897/pdf/multi0page.pdf