Matt,
A *very* difficult question. Lots of work has been done on this by many
different disciplines.
The most quantitative comes from utility theory, which has suggested
approaches such as standard gambles, time-trade-off, healthy-year
equivalents, etc. Utility makes the scale a probability, ie all
intermediate values are equivalent to a gamble between death now and a
normal healthy life. But there are *lots* of problems in implementing this
nice theory. If you search on standard gamble and time trade-off you'll
come across a lot of this.
Jane Weeks did a nice chapter in our book * on comparing the current
approaches.
Paul Glasziou
*Hunink M, Glasziou P, et al. Decision making in health and medicine.
Integrating evidence and values. Cambridge: Cambridge University Press, 2001
At 09/02/2005, Matt Williams wrote:
>Dear All,
>
>I'm a bit stuck on a problem with QoL.
>
>I started by thinking about mortality, where a figure (40%) seems to
>have a clear referent (if I take 1000 of you, 400 are dead in x years).
>In fact, this interpretation seems to give a semantics to the mortality
>figure which is grounded in an objective reality (after all, you're
>either dead or not).
>
>QoL doesn't seem quite so simple. Despite the fact that we agree that it
>exists, and that it can vary, and that some things would make it better
>or worse, I'm not sure what a QoL of 40/100 would mean - even if the 100
>point scale were well validated, etc.
>
>I've only been able to think of two ways of dealing with this:
>1: Ground everything in functional aspects - how far can you walk, how
>often are you sick, etc.
>
>2: Accept we don't really know what someone's absolute QoL is, but look
>instead at whether it is likely to go up or down from here. So, if you
>have flu, and take some paracetamol, I don't know what your QoL is, and
>I don't know what it is going to be, but I can strongly suspect that it
>is going to be better than it is now.
>
>The underlying problem is that there doesn't seem to be an objective
>referent (as in mortality) for us to hang the interpretation on.
>
>Does anyone else have any ideas?
>
>Thanks,
>Matt
>--
>Dr. M. Williams MRCP(UK)
>Clinical Research Fellow
>Cancer Research UK
>+44 (0)207 269 2953
>+44 (0)7384 899570
Paul Glasziou
Department of Primary Health Care &
Director, Centre for Evidence-Based Practice, Oxford
ph: 44-1865-227055 www.cebm.net
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