Julie,
Thanks for the stimulating question. The responses so far have been most
helpful.
Following a suggestion in the Altman reference that Eric Harvey pointed us
to, your problem might be eased by quoting the confidence interval as either:
1. NNT 4.65 (95% CI 2.3 to infinity to NNTH -390) - which Dave Sackett's
response spells out, or
2. NNT 4.65 (95% CI 2.3 to infinity+) indicating harm is a possibility, but
not spelling out how harmful. My prefence is the latter, as it is less
cumbersome, though slightly less informative than (1).
Paul Glasziou
At 09:28 AM 9/4/99 -0700, Julie Brown wrote:
>I am hoping for a little statistical guidance with the 95% CI around an
>NNT.
>
>Here are the specifics I am working with: The CER is 0.8, the EER is
>0.585, so the ARR is 0.215. The CI around the ARR is -0.00256 to 0.433.
>So far this makes sense to me. Now, the NNT = 4.65, but taking 1/ARR for
>the confidence limits, I get a 95% CI on my NNT of -390 to 2.3. This
>doesn't even include my value of 4.65, and doesn't intuitively make sense.
>
>What am I doing wrong?
>
>Julie Brown, MD
>Pediatric Emergency Medicine Fellow, box CH-04
>Children's Hospital and Regional Medical Center
>Seattle, WA 98105
>e-mail: [log in to unmask]
>fax: 206 527 3892
>
Paul Glasziou
Social & Preventive Medicine,
Medical School, Herston Rd,
Herston Qld 4006,
AUSTRALIA
PH 61-7-33655427 FAX: 61-7-33655442
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