Statistics from Altmetric.com
The complementary concepts QALYs and DALYs combine years of life and quality of life in a single measure.1–3 In Arnesen and Nord’s words: “QALYs are years of healthy life lived; DALYs are years of healthy life lost. Both approaches multiply the number of years (x axis) by the quality of those years (y axis). QALYs use “utility weights” of health states; DALYs use “disability weights” to reflect the burden of the same states. If the utility of deafness is 0.67, the disability weight of deafness is 1–0.67 = 0.33. Disregarding age weighting and discounting, and assuming lifetime expectancy of 80 years, a deaf man living 50 years represents 0.67×50 = 33.5 QALYs gained and 0.33×50+1.0×(80–50) = 46.5 DALYs lost”.2 Note that QALYs+DALYs = 33.5+46.5 = 80.0 = lifetime expectancy (complementariness).
More accurately, we had to put QALYs = (0.67)×(50y) = 33.5y and DALYs = (0.33)×(50y)+(1.0)×(80y–30y) = 46.5y. This means that the unit of measurement of QALYs and DALYs is years (y). As y is the unit for lifetime, using the same unit for the product (lifetime)×(lifequality) is confusing.
Saying that quality is rated on a scale from 0 to 1, we have implicitly transformed the real but unknown scale of quality into a standard scale, where 0 denotes no quality at all and 1 the 100% of quality expected (lifequality expectancy). Therefore QALYs and DALYs, combining actual years and dimensionless quality, are, in fact, semi-standardised measures. In a previous article we proposed the fully standardised measures SQALYs/SDALYs.4 This article, unstandardising lifequality as well, proposes the fully unstandardised measures UQALYs/UDALYs.
Let q be the unit of measurement of quality—qualio in singular, qualia in plural. Continuing the example above, let us assign lifequality expectancy 160q to dimensionless 1, and lifequality 107q to 0.67—in the same manner as dimensionless 1 was previously4 assigned to lifetime expectancy and 0.625 to 50y. Thus, fully unstandardised QALYs = UQALYs = (107q)×(50y) = 5350qy, and fully unstandardised DALYs = UDALYs = (160q–107q)×(50y)+(160q)×(80y–50y) = 7450qy. That is, from the total expected life to be lived = (160q)×(80y) = 12800qy = life expectancy, 5350qy were actually lived and 7450qy were lost: 42% and 58% respectively, the same as in fully standardised measures.4
These transformed to fully unstandardised measures do not measure life in years as if it was only lifetime, but, as it is the product (lifetime)×(lifequality), in qualia-years (qy); therefore UQALYs/UDALYs are not misleading. The idea is analogous to py (pack years) in smoking measuring.
Concluding, current semi-standardised QALYs/DALYs should be replaced by either fully unstandardised or fully standardised ones—the latter, in addition, are more understandable and comparable.4
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