In message <[log in to unmask]>, Martin Dawes
<[log in to unmask]> writes
>
>I see a difference in the population approach of NNT's and NNH's to the
>strategic apporach to care in the individual. If one has a selection of
>alternative therapies why don't we try them. This would avoid the problem of
>"drug failure" which usually is interpreted as doctor failure when the 1st
>drug is not succesful. I mean we talk about NNT's of 4 as great. yet that
>means 3 individuals dont reach the arbitrary threshold.
>
It doesn't though does it? Not in real life. If you have a group of 4
individuals and they are given a drug which produces an absolute risk
reduction of 25% for a particular event, any number of them from 0 to 4
could have the event prevented. The probability of any particular number
having the event prevented will follow the binomial distribution.
No doubt this explains why, even if the ARR is small, if a large number
of small groups of patients are treated with a drug, then in some groups
a much higher proportioin of patients will have successful outcomes than
would be expected from population based data. So in the case of MS you
are bound to have a few neurologists with, say, 30 or 40 MS patients,
whose experience is that 70% or 80% have responded to beta interferon.
These will then extrapolate falsely from their experience and become
advocates of the drug's use. Of course the majority of neurologists will
find that their success rate is not too far from the 10% or 15%
predicted from RCTs and some will find it much lower. I guess it is also
likely that patients whose treatment is successful might be more likely
to continue follow up, which will bias the neurologist's opinion in
favour of the treatment (does anyone know whether this has been
researched?)
Toby
--
Toby Lipman
General practitioner, Newcastle upon Tyne
Northern and Yorkshire research training fellow
Tel 0191-2811060 (home), 0191-2437000 (surgery)
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