Future health (prognosis)
(ii) Severity = Tu – Td (Life expectancy at the time of diagnosis)
The second definition assesses the degree of severity on the basis of remaining life expectancy in the absence of treatment (Tu – Td), and can also be justified in terms of the patient’s acute need for help (rule-of-rescue). According to this definition, a short remaining life expectancy is deemed more serious than when the prognosis is longer. British health authorities emphasise such «end-of-life» assessments (10). Both of these first definitions have only one dimension of health and are therefore overly simplistic. For example, 1 – Hd ignores prognosis in relation to survival, while Tu – Td ignores acute need for pain relief.
(iii) Severity = A3 (Quality adjusted life expectancy at time of diagnosis)
A third possibility is to assess the prognosis as a combination of health-related quality of life and remaining life expectancy with no treatment (the area A3). This alternative is perhaps closest to the definition of severity proposed by the Lønning II Commission (3), and it is also recommended in the Directorate of Health’s manual for economic evaluation (11). In the literature, «severity» is used to refer to definitions (i), (ii) and (iii) alike (8). In principle, one could argue that Tu – Td is independent of age (4). Often, however, the prognosis will be affected by the patient’s age, for example with regard to most forms of cancer (12). At an advanced age, when the life expectancy of a healthy person (T*) is shorter than the expected prognosis of an average patient (T* – Td) < (Tu – Td), the correlation between age and severity is very high.
Two alternative definitions assess the severity of the disease on the basis of future health in a more sophisticated manner:
(iv) Severity = (T* – Tu) / (T* – Td) x 100 % (Relative future loss of years of life)
(v) Severity = B2/(A3+B2) x 100 % (Relative future loss of quality adjusted life years)
These two definitions are concerned with the realisation of the patient’s health potential. This is calculated as the fraction of the health loss with disease over the remaining health in the absence of disease at the time of diagnosis, based either on years of life (iv) or quality adjusted life years (v). According to this definition, severity is an expression of how much of his or her future health the patient loses as a result of the disease, i.e. the proportional shortfall of health (13). Dutch researchers have proposed proportional shortfall as a priority setting criterion (14).
According to this definition, previous health is seen as irrelevant, and proportional shortfall thus ignores the past disease burden of chronic sufferers, for example. In mathematical terms, proportional shortfall is a ratio, which has been criticised for concealing the magnitude of this health loss (15). A health loss of five days when life expectancy is ten days is deemed just as serious as a health loss of five years when life expectancy is ten years. In the Norwegian debate, it has been argued that proportional shortfall is an age-neutral definition for severity (16). This is incorrect. On the contrary, with this principle «severity» will increase with age, because the area B2 shrinks with age and because B2 is below the fraction bar in (v). While this is a relatively trivial mathematical observation, it has ethical implications that are problematic to many. Using a reference age of 80 years, as proposed by the Norheim Commission, proportional shortfall implies that the loss of a quality adjusted life year for a 78-year-old (e.g. prostate cancer) will be deemed 40 times more «severe» than the loss of a quality adjusted life year for a one-year-old (e.g. childhood cancer) (Table 1). To the extent that the health loss criterion represents «age discrimination», we can therefore say that proportional shortfall is «reverse age discrimination».
Table 1
The relationship between age and severity when the future health loss is one good year of life for all, and when proportional shortfall is used as the definition. The example shows that relative future health loss amounts to «reverse age discrimination» and that the relative priority given to elderly people increases exponentially
Patient (age) |
Future good years of life without illness (A3+B2) |
Future health loss (B2) |
Severity = B2/(A3+B2) (%) |
Relative priority |
1 year |
79 |
1 |
1.3 |
1.0 |
10 years |
70 |
1 |
1.4 |
1.1 |
40 years |
40 |
1 |
2.5 |
2.0 |
70 years |
10 |
1 |
10 |
7.9 |
78 years |
2 |
1 |
50 |
40 |
Instead of a fixed reference age, we can use remaining life expectancy at different age levels, i.e. based on life expectancy tables (17). This reduces the effects for relative priority at an advanced age, but does not change the fact that the method represents «reverse age discrimination» and that the relative priority increases exponentially with age (Table 2).
Table 2
The relationship between age and severity when future good years of life are based on a life table (17) instead of a fixed reference age
Patient (age) |
Future good years of life without illness (A3+B2) |
Future health loss (B2) |
Severity = B2/(A3+B2) (%) |
Relative priority |
1 year |
80.9 |
1 |
1.2 |
1.0 |
10 years |
71.9 |
1 |
1.4 |
1.1 |
40 years |
42.6 |
1 |
2.4 |
1.9 |
70 years |
16.0 |
1 |
6.0 |
4.9 |
78 years |
10.3 |
1 |
10 |
7.7 |
RE: Alder og alvor
21.08.2015Bjarne Robberstads drøfting av alder og alvor (1) er teknisk interessant, men jeg mener han skaper forvirring ved ikke å skille mellom hva et godt etablert uttrykk som «en tilstands alvorlighet» betyr i medisin og hvilken vekt man kan ønske å legge på ulike…