Signature
DW = N_life / N_cure
| Inputs | Definition | Unit |
|---|---|---|
N_life | Number of people whose lives are prolonged, such as 1,000 | people |
N_cure | Number of people cured of the condition judged equal to the reference, at least N_life | people |
DW | Weight implied by the cure equivalence | none |
|---|
Function
Disability weight scaling of time lived with a non-fatal health state
Maps time lived in a non-fatal health state to healthy time lost by multiplying it by the state's disability weight, on a scale where 0 is equivalent to full health and 1 to death. The products give years lived with disability (YLD), which add to years of life lost to give DALYs. When people have several conditions, weights are combined multiplicatively and the combined loss is shared among the conditions. The notation follows the Disability Weight article.
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Implementations
Excel
Second person trade-off weight from named numbers
With LivesProlonged and CuresEquivalent named, the formula returns the weight, held in PTOTwoWeight.
=LivesProlonged/CuresEquivalent
Assumptions
Cure removes the whole disability weight in the second person trade-off
A cure returns a person to full health for the period valued, so the health gained per cure equals the weight.
Worked examples
GBD 1990 person trade-off example of 5,000 cures of blindness
If 5,000 cures of blindness are judged equal to prolonging the lives of 1,000 people, the weight is 1,000 / 5,000, or 0.2.
N_life = 1000; N_cure = 5000; DW = 0.2
Second person trade-off disability weight for a condition judged half as bad as death
If 2,000 cures are judged equal to 1,000 lives prolonged, the weight is 0.5 (computed here for illustration).
N_life = 1000; N_cure = 2000; DW = 0.5
Common errors
Inverting the second person trade-off ratio
Dividing cures by lives gives 5 for blindness in the example, outside the scale; the weight is lives over cures.
Sources
Second person trade-off weight of 0.2 for blindness
Arnesen T, Nord E. The value of DALY life: problems with ethics and validity of disability adjusted life years. BMJ. 1999;319(7222):1423-1425. doi:10.1136/bmj.319.7222.1423. Section on the person trade-off: PTO2 asks how many people cured of a chronic condition equal prolonging the lives of 1,000 people; a response of 5,000 for blindness gives a weight of 1,000:5,000 = 0.2; unlike PTO1 it does not presuppose that disabled people's lifetime is devalued.
Canonical Identity
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