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Expected outcome decision
makers choose the decision alternative with the highest expected
outcome. (To review this topic, go to Expected
Value Decision Making).
Determining the expected
outcome in people with serious illness requires some adjustments
to take account of the effect of the illness on the person's life
expectancy. One way to say this is:
The expected value
of a treatment is the probability of each of the possible outcomes
of the treatment times the size of the corresponding outcome,
summed over all of the different outcomes of the treatment.
A chance node illustrates
this point. At this chance node, any of three outcomes, A, B,
or C, can occur by chance with probabilities p[A], p[B], or p[C]
respectively.
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3.6.1: A Chance Node
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The expected
value at this chance node is: p[A]*A + p[B]* B + p[C]* C, where
A, B, and C are the desirability of these outcome states.
The most commonly used
measure of the magnitude of the outcome A is quality-adjusted
life years (QALYs). (For more on QALYs, go to Assigning
Utility.)
QALY = life expectancy
(in outcome state A) * utility[outcome state A]
QALY = LE[A]*U[A]
How might the QALYs
of a person with serious chronic illness differ systematically
from those of a person who is healthy?
- Utility of a
health state - It is certainly possible that the utilities
of a person with serious chronic illness might differ systematically
from a healthy person. Someone with a serious chronic disease
might attach a lower utility to health states related to another
disease, simply because that health state is less desirable
as a result of their chronic disease.
- Life expectancy
in a health state - The life expectancy of a person with
serious chronic illness is usually shorter than a healthy person
of the same age.
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