What is a DALY?

The Disability-Adjusted Life-Year (DALY) is a metric that combines the burden of mortality and morbidity (non-fatal health problems) into a single number.1 It is the primary metric used by the World Health Organization to assess the global burden of disease,2 and the primary metric used by projects such as the Disease Control Priorities report3 to quantify the cost-effectiveness of different programs.

We fully explain the formula and meaning of the DALY metric in a series of posts on our blog, here.

What are the limitations of the DALY metric? Why does GiveWell not focus on it?

The DALY metric is used to provide a single number to capture all of the health costs caused by a disease (or averted by an aid program). 1 DALY could represent 1 year of life lost (due to early death), 1.67 years spent with blindness, 5.24 significant malaria episodes, 41.67 years spent with intestinal obstruction due to ascariasis (a parasite), or many possible combinations of these and other symptoms.4 There is no way of knowing, from just how many DALYs a program is said to have averted, whether it has saved lives, prevented large numbers of minor health problems, or some combination thereof.

We feel that this creates a number of problems for donors seeking the charity that best fits their values. More in our blog series on DALYs, available here.

Interpreting the DALY metric

The Disease Control Priorities report frequently estimates the cost-effectiveness of different programs in terms of cost per DALY averted. We seek to convert these figures, using fairly minimal assumptions, into numbers that have clearer and more intuitive meanings, including:

• Years of a given symptom (blindnesss, skin disease, etc.) averted
• Cases of a given health condition (blindness, skin disease, etc.) averted

In some cases, our conversion calculation is simple enough to explain fully in a footnote. In other cases, we use a calculation that is still simple but has several steps and is shared across many estimates, so we use the following spreadsheet:

• DalysToSymptoms.xls (Excel 2000 format)

Sources

• Disease Control Priorities Project. 2006a. "Disease Control Priorities in Developing Countries (2nd edition)." Available online at http://www.dcp2.org/pubs/DCP, accessed 7/8/09.
• Disease Control Priorities Project. 2006b. "Global Burden of Disease and Risk Factors." Available online at http://www.dcp2.org/pubs/GBD, accessed 7/8/09.
• World Health Organization. Organization website. Online at http://www.who.int/en/, accessed 7/9/09.

1. 1.

   GBD 2006, page 47.

2. 2.

   See http://www.who.int/healthinfo/global_burden_disease/en/index.html, accessed 7/8/09.

3. 3.

   DCP 2006, Pg 26, Box 1.4.

4. 4.

   These numbers are based on the DALY formula (described with references on our blog here) and the official Disability Weights found in GBD 2006, Table 3.A.6 (http://dcp2.org/pubs/GBD/3/Table/3.A6, accessed 7/8/09).