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EVIDENCE-BASED-HEALTH  January 1999

EVIDENCE-BASED-HEALTH January 1999

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Subject:

RE: NNT or NNH

From:

"Djulbegovic, Benjamin" <[log in to unmask]>

Reply-To:

Djulbegovic, Benjamin

Date:

Mon, 25 Jan 1999 16:00:44 -0500

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (72 lines)

	We have recently integrated evidence-based summary therapeutic
measures within a decision analytic model and found that in prophylactic
treatment setting
(that is, Rx vs NoRx) , action threshold (AT)=NNT/NNH.
	 AT is the probability of the clinical event (eg. disease) at which
you should be indifferent between Rx vs NoRx. If the probability of the
disease is above AT, then you should give the treatment; if it is below, you
shouldn't.  By the same token, the treatment should NEVER be given if
NNT>NNH (or risk of the treatment >RRR) (since AT cannot be>1). Similarly,
we should NEVER order Dx. test if the treatment risks >RRR (relative risk
reduction). Details of our model were presented last year at the Society for
Med Decis Making, and are published in Comp Biomed Res and Cancer Control,
and can be assessed through the following web sites
http://www.hsc.usf.edu/~bdjulbeg/Programs/BR/br-java.htm (featuring the
program to calculate clinical action thresholds) and
http://www.moffitt.usf.edu/pubs/ccj/v5n5/article2.html. (For the choice
between Rx1 vs Rx2, the equations are more complicated and can be found at
the web sites given above).

hope this helps

ben djulbegovic
-----

Benjamin Djulbegovic, MD
Associate Professor of Medicine
H. Lee Moffitt Cancer Center & Research Institute
at the University of South Florida
Division of Blood and Bone Marrow Transplant
12902 Magnolia Drive
Tampa, FL 33612

e-mail:[log in to unmask]
http://www.hsc.usf.edu/~bdjulbeg/
phone:(813)979-7202
fax:(813)979-3071

> -----Original Message-----
> From:	Andrew Jull [SMTP:[log in to unmask]]
> Sent:	Monday, January 25, 1999 3:30 PM
> To:	[log in to unmask]
> Subject:	NNT or NNH
> 
> Dear All
> 
> I had a discussion with a colleague recently as to the use of NNT or NNH
> when the outcome is harm ie wound infection. I have not been able to find
> any "rules" on when to use NNT as opposed to NNH, so have had to apporach
> their use deductively. Briefly, I believe that NNT should be used when the
> ARR is positive (and therefore is a reduction in the incidence of harmful
> outcome). On the other hand NNH should be used when the ARR is negative
> (actually an absolute risk increase, and therefore there is an increase in
> the incidence of harmful outcome).
> 
> However, my colleague has pointed out that semantically this makes litle
> sense; where the outcome is harm, then NNH should be used. Where the
> outcome
> is beneficial, then NNT should be used. Essentially this would mean when
> there was risk increase, NNH would always be used, but when there was risk
> reduction, either NNH or NNT would be used depending on whether or not the
> outcome was harm, thus enhancing the terms' communicative meaning.  I can
> see that this might make more sense from a user's point of view and would
> welcome the list's views on this.
> 
> regards
> Andrew Jull
> Clinical Nurse Consultant
> Auckland Hospital
> NEW ZEALAND


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