I think it is an excellent question - one that doesn't get asked often
enough.
I've always approach this issue by first asking if the baseline risk changes
over time or is relatively constant year-to-year.
If you believe there are significant changes in baseline risk over time,
than I would suggest you calculate the ARR and NNT over the multiple year
follow up period.
If you believe that the risk is relatively constant over time, than it seems
reasonable to calculate ARR and NNT on a exposure-year basis.
Regards,
Eric Harvey
----- Original Message -----
From: "Lubna A. Al-Ansary" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, September 27, 2002 6:19 AM
Subject: NNT & patient-years
> Dear All,
> You might consider this a naive question but I could
> not find an answer in any of the EBM resource that I
> have & therefore I would greatly appreciate your help.
> In prospective trials that run for many years, would
> it be more accurate/useful to calculte the number
> needed to treat (NNT) in reference to the absolute
> risk reduction (ARR) in general or in reference to the
> ARR in patient-years?
> Thanks in advance.
> Yours sincerely,
> Lubna
>
> =====
> Dr.Lubna A.Al-Ansary, MSc, FRCGP
> Associate Professor
> Dept of Family & Community Medicine
> College of Medicine, King Saud University
> P.O.Box 2925, Riyadh 11461
> SAUDI ARABIA
> Email: [log in to unmask]
>
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