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EVIDENCE-BASED-HEALTH  March 2006

EVIDENCE-BASED-HEALTH March 2006

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Subject:

Some numbers on NNT, NTN and ITI

From:

Moacyr Roberto Cuce Nobre <[log in to unmask]>

Reply-To:

Moacyr Roberto Cuce Nobre <[log in to unmask]>

Date:

Sun, 19 Mar 2006 20:29:44 -0300

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (244 lines)

Dear Prof Attia, I understand that the new index NTN is perfect. Two hypothetic
examples of two different trials, with different mortalities, and the same
absolute risk reduction						

trial 1				trial 2			
group A	group B			group A	group B		
100	100	alive baseline	100	100		
8	5	dead endpoint	82	79		
92	95	alive endpoint	18	21		
	3	    ARR		3		
	33,33	    NNT		33,33		
92+5/3= 32,33	    NTN		32,33	=18+79/3	
100-3=	97	    ITI		97	=100-3	

Cheers

Moacyr
__________________________
Moacyr Roberto Cuce Nobre
Unidade de Epidemiologia Clínica
InCor - HCFMUSP
fone/fax: 55 11 3069-5941
celular : 55 11 9133-1009



Citando "Dr. Abdelhamid Attia" <[log in to unmask]>:

 Dear Prof. Dan,
 
 I can't agree more with your reasoning. You are 100% correct when we put these
 terms in their normal perspectives as terms comparing two interventions. If
 you read my 2nd paragraph again I wrote: "I find these two new indices, as
 such, misleading."
 
 My students are always troubled reading about the NNT because it is almost
 always phrased in sentences that give the impression as if it is an absolute
 number although it should be a relative one comparing 2 interventions. I
 always believe that we should stress in our writing about the NNT on the two
 interventions being compared e.g. (dexamethasone Vs. budesonide for the
 treatment of croup) This should follow the NNT immediately.
 
 What is even better is to add the absolute numbers between 2 brackets after
 the NNT. For example the NNT is 33 (32 dexamethasone / 31 Budesonide for the
 treatment of croup) or the NNT is 33 (17 dexamethasone / 16 budesonide for the
 treatment of croup). This gives a global view about the effects of both
 compared interventions in one easy to comprehend sentence.
 
 Same way this should be clear in the new indices NTN and ITI. This is the only
 way every one who reads these numbers can get their meanings clear. 
 
 The lack of the above caused the confusion of Jon, to whom I responded, who
 said "From a patient perspective I wonder how the interplay of 'most effective
 intervention' might fit with an ITI of 97% or a NTN of 32.
 
 I think that confusing terms need more attention to details to make them
 easier to comprehend.
 
 Best of wishes and thank you also for a thought provoking response.
 
 Abdelhamid Attia
 
 Prof. Dr. Abdelhamid Attia
 Prof. of Ob & Gyn, Cairo University
 President; Arab Federation of EBM
 Executive Director, Center of EBM, Cairo University
 
 ----- Original Message ----- 
 From: "Dan Mayer" <[log in to unmask]>
 To: <[log in to unmask]>
 Sent: Thursday, March 16, 2006 4:38 PM
 Subject: Re: Best EBM methods papers for 2005?
 
 
 > Dear list:
 > 
 > Re: Professor Attia's Discussion
 > 
 > I want to thank Professor Attia for his thought provoking question and
 > respond to his discussion about Number Treated Needlessly and Index of
 > Therapeutic Impotence.  I think that the final numbers should be
 > interpreted in a different way.
 > 
 > If 32 patients are treated successfully with the experimental drug out
 > of every 33 compared to 31 out of every 33 in the control group, the
 > Number Needed to Treat is 33.  
 > 
 > The Number Treated Needlessly (NTN) is a little more complicated and I
 > think that your reasoning is incorrect because of the way that our
 > brains think about numbers.  Successful treatment occurred in 32 out of
 > 33 patients with the intervention and 31 out of every 33 in the control
 > group.  That leaves 1 additional patient in the 33 treated with either
 > treatment that obtained benefit with the experimental treatment and
 > would not have with the control treatment.  We can only say that 31
 > patients out of the 33 were treated with a useful therapy.  They got
 > better with the control therapy and did as well as the 31 out of 33 that
 > were treated in the experimental group and one patient in each group
 > didn't respond.  Finally, it was only that one additional patient out
 > of 33 that did better with the experimental group.
 > 
 > It may be more helpful to think of NTN as all those patients who were
 > treated who would do just as well with either therapy.  In this example,
 > it is 32 out of every 33 treated.  Index of Therapeutic Impotence (ITI)
 > can be thought of as the ratio of all those who get better or no better
 > (i.e., do the same) with both therapies divided by all the patients we
 > would need to treat to have one additional good outcome.  This tells us
 > the percentage of patients that go no improvement specifically because
 > of the experimental therapy.  It is a more realistic and easily
 > understood concept (by patients) than NNT.
 > 
 > In the second example there are 17 patients out of 33 that were treated
 > successfully in the experimental group compared to 16 out of 33 in the
 > control group.  The NNT remains 33.  One additional patient out of 33
 > benefited from the therapy.  For every 17 of 33 patients who were
 > treated successfully with the intervention there were 16 out of 33
 > patients treated successfully without the intervention so that one more
 > patient out of 33 was treated successfully with the intervention than
 > without.  There were 16 in each group who didn't achieve any success
 > from therapy or control.  The Number Treated Needlessly is still 32 out
 > of 33 (16 benefited and 16 didn't in each group) since only one
 > patient out of 33 gets benefit, meaning the other 32 don't.  The end
 > result is the same with 3% of patients more likely to respond to the
 > intervention than the control and 97% of the patients treated with the
 > intervention being no more likely to respond to the treatment any better
 > than the control.  This is the ITI.  ITI can also be seen to be one
 > minus the Absolute Rate of Reduction.  I believe it is a very useful
 > number because it really does tell you how useless the drug is.
 > 
 > Hope this helps,
 > 
 > Best wishes,
 > 
 > Dan
 > 
 >
 ****************************************************************************
 > Dan Mayer, MD
 > Professor of Emergency Medicine
 > Albany Medical College
 > 47 New Scotland Ave.
 > Albany, NY,  12208
 > Ph; 518-262-6180
 > FAX; 518-262-5029
 > E-mail; [log in to unmask]
 >
 ****************************************************************************
 > 
 > >>> "Dr. Abdelhamid Attia" <[log in to unmask]> 3/9/2006 8:03 PM >>>
 > Dear Jon and all Listers,
 > 
 > Regarding Jon's query about the number treated needlessly (NTN) or the
 > index
 > of therapeutic impotence (ITI) in Bogaty's article I have an opinion
 > that I
 > want to discuss with you.
 > 
 > First, I only read the abstract but not the whole article but I find
 > these
 > two new indices, as such, misleading. That's why Jon asks his
 > question.
 > 
 > The NNT is the number of patients needed to be treated by a given
 > treatment
 > to get one "MORE" benefit than another treatment, or a placebo, in the
 > control group.
 > 
 > So if 33 is the number needed to treat for a given drug "compared to
 > another" we can not say that we have 32 who failed to be treated with
 > it so
 > that the NTN is 32 and the ITI is 97%!
 > 
 > We may have 32 patients who are treated successfully out of every 33
 > patients in the intervention group compared to 31 out of every 33 in
 > the
 > control group. In this situation the NNT is 33 but the ITI (for the
 > intervention) is 1/33 which is 3% actually.
 > 
 > The same indices will change with the change of the numbers treated
 > successfully for the same NNT. If we have 17 patients treated
 > successfully
 > out of every 33 patients in the intervention group compared to 16 out
 > of
 > every 33 in the control group. In this situation the NNT is 33 but the
 > ITI
 > is 16/33 which is 48.5%.
 > 
 > Any opinions on this?
 > 
 > Best of wishes,
 > Abdelhamid Attia
 > 
 > Prof. Dr. Abdelhamid Attia
 > Prof. of Ob & Gyn, Cairo University
 > President; Arab Federation of EBM
 > Executive Director, Center of EBM, Cairo University
 > 
 > 
 > 
 > 
 > 
 > 
 > 
 > ----- Original Message ----- 
 > From: "Jon Brassey" <[log in to unmask]>
 > To: <[log in to unmask]>
 > Sent: Sunday, March 05, 2006 10:51 AM
 > Subject: Re: Best EBM methods papers for 2005?
 > 
 > 
 > > Dear All,
 > >
 > > I must thank Michael for bringing that Bogaty and Brophy article.  I
 > haven't come across this article, or reference to it.
 > >
 > > Is anyone aware of this being discussed at great depth anywhere? 
 > Does
 > anyone have an opinion on it?  From a patient perspective I wonder how
 > the
 > interplay of 'most effective intervention' might fit with an ITI of 97%
 > or a
 > NTN of 32.
 > >
 > > Cheers
 > >
 > > jon
 > >
 > >
 > > -----------------------------------------
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