Signature
YLD = P * DW
| Inputs | Definition | Unit |
|---|---|---|
P | Number of people living with the sequela during the year, equal to person-years for a one-year period | people |
DW | Severity of the state on a scale from 0 (equivalent to full health) to 1 (equivalent to death) | none |
YLD | Healthy years lost to the sequela in one year | years |
|---|
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
Years lived with disability from named cases and weight
With prevalent cases in PrevalentCases and the weight in DisabilityWeight, the formula returns the YLDs, held in YLDCondition. For several sequelae in columns, =SUMPRODUCT(CasesRange,WeightRange) adds them before any comorbidity adjustment.
=PrevalentCases*DisabilityWeight
Assumptions
Prevalence-based YLD without age weighting or discounting
Since GBD 2010, YLDs are prevalence times disability weight with no age weighting or discounting; the GBD 1990 incidence-based form with a 3 per cent discount rate and age weights gives different numbers.
One named weight set for every sequela
All weights come from one set (for example GBD 2013), because revised health-state descriptions moved some weights sharply between rounds.
Worked examples
Condition A affecting 1,000 people with a weight of 0.10
In the article's illustrative population, 1,000 people with condition A at a weight of 0.10 give 100 YLDs, before any adjustment for comorbidity.
P = 1000; DW = 0.1; YLD = 100
Condition B affecting 500 people with a weight of 0.30
Five hundred people with condition B at 0.30 give 150 YLDs; with condition A the unadjusted total is 250.
P = 500; DW = 0.3; YLD = 150
Complete hearing loss under the GBD 2010 and GBD 2013 weights
For 1,000 people with complete hearing loss, the GBD 2010 weight of 0.033 gives 33 YLDs and the revised GBD 2013 weight of 0.215 gives 215 (computed here for illustration), so the weight set alone changes the burden more than sixfold.
P = 1000; DW = 0.215; YLD = 215
Common errors
Entering 1 minus a utility value as the disability weight
Disability weights and QALY utility weights come from different tasks and constructs, so 1 minus a utility value is not a disability weight, and the reverse conversion is not a QALY weight.
Mixing weight sets
GBD 2010, GBD 2013 and WHO revisions differ for some states; complete hearing loss moves from 0.033 to 0.215, so a study must name its set.
Sources
GBD 2010 YLDs as prevalence times disability weight
Vos T, Flaxman AD, Naghavi M, et al. Years lived with disability (YLDs) for 1160 sequelae of 289 diseases and injuries 1990-2010: a systematic analysis for the Global Burden of Disease Study 2010. The Lancet. 2012;380(9859):2163-2196. doi:10.1016/S0140-6736(12)61729-2. Methods: YLDs are computed as the prevalence of a sequela multiplied by the disability weight for that sequela without age weighting or discounting; YLDs for a disease or injury are the sum of the YLDs for its sequelae.
WHO prevalence YLD per cause from disability weight and prevalence
World Health Organization. WHO methods and data sources for global burden of disease estimates 2000-2019. Global Health Estimates Technical Paper WHO/DDI/DNA/GHE/2020.3. Geneva: WHO; 2020. Section 2: age weighting and time discounting dropped and YLDs calculated from prevalence rather than incidence, adjusted for independent comorbidity; equation 2, YLD_i = DW_i x p_i.
GBD 2010 and GBD 2013 disability weights for complete hearing loss
Salomon JA, Haagsma JA, Davis A, et al. Disability weights for the Global Burden of Disease 2013 study. The Lancet Global Health. 2015;3(11):e712-e723. doi:10.1016/S2214-109X(15)00069-8 (abstract read). Results: weights common to GBD 2010 and GBD 2013 were highly correlated (r 0.992), but revised health state descriptions changed some weights substantially, including complete hearing loss, 0.033 in GBD 2010 and 0.215 in GBD 2013.
Canonical Identity
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