Dr. Davis,
In my view, the crux of this matter is establishing a threshold or critical
point in your outcome measure, ie., an estimate of the minimum clinically
important change. Once you have this, say 0.5 days, you can estimate the
proportion of patients achieving this threshold in each group, the ARR, and
the NNTs.
It may not be as simple as that for parallell group RCTs. You may want to
see Guyatt's neat paper on this in BMJ 1998;316:690-693.
There was a lead on this a few weeks ago in this discussion list.
cheers.
Samuel Wiebe
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
At 03:55 PM 99/04/01 -0800, you wrote:
>Can one of the participants on this list point us to a good discussion
>on the proper 'framing' of NNT in the context of a continuous outcome
>measure.
>
>For example, a rather bright fellow has posed this question to me:
>Treatment "X" shortens the hospital stay for disease "Z" by 0.50
>hospital days. Is there a relevant way to present this that is roughly
>equivalent to a NNT?
>
>I thought, off hand, that this would be somewhat equivalent to
>suggesting that 2 children would have to be treated to 'save' one
>hospital day. Fundamentally this appears overly simplistic, but I would
>be interested in hearing how others might have dealt with this before.
>
>Thanks in advance,
>
>Robert L. Davis, MD, MPH
>Pediatric Evidence Based Program
>Department of Pediatrics
>University of Washington
>Seattle, WA , USA
>
++++++++++++++++++++++++++++++++++++++
Samuel Wiebe MD, MSc, FRCPC
Assistant Professor
Clinical Neurological Sciences
Epidemiology and Biostatistics
University of Western Ontario
London, Ontario, CANADA
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