5.5 Quantifying severity of disability
As previously mentioned, the YLDs in DALYs are calculated using a numerical factor or weight that accounts for the severity of the health condition. These disability weights are measured on a scale from 0 to 1, where 0 equals a state of full health and 1 is equivalent to death.
Helpfully, the Global Burden of Disease study produced a set of disability weights that can be used for economic evaluations (GBD, 2021). The disability weights in this dataset cover a broad range of health conditions and can be applied to any country or setting.
Activity 7: Calculating DALYs from a sample dataset
Look at the information in Table 5, which presents information on four healthcare strategies for a health condition. The strategies include current practice and three new strategies (A, B and C). The strategies are all used for the same type of patients and impact both their life expectancy and the symptoms of the disease.
Calculate the estimated number of DALYs for each of the four strategies by completing the ‘DALYs’ column in Table 5.
Additional key information: The average life expectancy for the general population is 65 years, and the disability weighting for this health condition is 0.4.
Hint: Remember the information from Section 5.4 about how to calculate DALYs. As a reminder, the formula is DALY = YLD + YLL, where YLD = years lived with disability and YLL = years of life lost.
| Interventions | Number of years lived (age at death) | Years of life lived with symptoms | DALYs |
|---|---|---|---|
| Current practice | 55 | 10 | |
| Strategy A | 55 | 6 | |
| Strategy B | 60 | 7 | |
| Strategy C | 58 | 5 |
Discussion
Table 6 shows the completed table.
| Interventions | Number of years lived (age at death) | Years of life lived with symptoms | DALYs |
|---|---|---|---|
| Current practice | 55 | 10 | 14 |
| Strategy A | 55 | 6 | 12.4 |
| Strategy B | 60 | 7 | 7.8 |
| Strategy C | 58 | 5 | 9 |
To calculate the DALY, first the YLD and YLL must be calculated. YLD is calculated by multiplying the number of years of life lived with symptoms by the disability weighting. For example, using the information in the question and in Table 5:
YLD = 10 × 0.4 = 4
YLL is calculated by subtracting the life expectancy with a health condition from the normal life expectancy. For example, using the information in the question and in Table 5:
YLL = 65 – 55 = 10
Now the DALY can be calculated as:
DALY = YLD + YLL
This would be:
DALY = 4 + 10 = 14
5.4 Disability-adjusted life years (DALYs)
