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Old 08-30-2012
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Stats Biostats Question

A trial shows that an antihypertensice med lowers 5yr risk for stroke from 8 per 1000 patients to 6 per 1000 pts, providing Relativ Risk Reduction of 25%. Based on this study, number of pts who must be treated to prevent the stroke is?

A. 4
B. 75
C. 250
D. 500
E. 2000

Plz give explanation and detailed calculations
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Old 08-30-2012
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N n t= 1/r r r

1/0.25= 4
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Thats not the Right answer
thats exactly what i did too
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nnt= 1/ARR

but how is it applicable here? anyone??
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Old 08-30-2012
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Quote:
Originally Posted by shyangel18 View Post
nnt= 1/ARR

but how is it applicable here? anyone??
Would be D , ARD= 0,008-0,006=0,002
Then nnt= 1/0,002= 500
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Old 08-30-2012
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Is the answer 500 i,e choice D
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Old 08-30-2012
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If 1000 patients are treated to save 2 patients

Then NNT=1000/2=500
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yes the Right answer is D!

v smart step enhancer. thats a good trick

but anders , thats the actual way to go about it. thanx!!
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Quote:
Originally Posted by step_enhancer View Post
If 1000 patients are treated to save 2 patients

Then NNT=1000/2=500
is this stratergy generalizable??
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Its should be ARR not ARD

ARR is absolute risk reduction.

ARR is The reduction in risk associated with treatment as compared to placebo

Here ARR =8/1000-6/1000
ARR=.002

NNT=1/ARR
=1/.002
=500

Or you can simply do how many u need to treat to save one live i.e 500
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Quote:
Originally Posted by shyangel18 View Post
is this stratergy generalizable??
I dont know ,may be ....

It depends on the question ,i also get confused .depends on how the question is worded .if its simple ,then we can use .
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Quote:
Originally Posted by step_enhancer View Post
I dont know ,may be ....

It depends on the question ,i also get confused .depends on how the question is worded .if its simple ,then we can use .
Hey! I applied the same logic rather than calculation (As they're not my forte)
And i got to the answer, IMHO It can be genaralized coz if you think about it, NNT is based on the principle of "How many you need to treat to save one life, right?! So if we are given the no. of pt fatalaties / incidents, We can conclude NNT by simple binary method.
Lemme know your thoughts!
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Quote:
Originally Posted by step_enhancer View Post
If 1000 patients are treated to save 2 patients

Then NNT=1000/2=500
logical thinking
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Old 09-06-2012
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Quote:
Originally Posted by shyangel18 View Post
is this stratergy generalizable??
I have been looking for the answer to your question and finally found the answer here

Apparently you can calculate the NNT from incidence rate- Kaplan LN CK Psych Page 110

calculate the ratio of incidence of disease, which is already given in this question as 8/1000 and 6/1000

calculate the difference of those ratio, which will be ARR

In this case, 8/1000-6/1000= 2/1000 = ARR


NNT= 1/ARR.

So, 1/ARR= 1000/2=500

Another way of doing it:



Step1) calculate the difference of incidence of disease (one subtraction)
8-6=2


Step2) divide your own sample size by difference of incidence of disease
(from step1)

1000/2=500

Bottomline:

If Incidence rate is given in the question then you can calculate NNT directly from it by 1/Incidence rate or 1/the difference of the Incidence rate.

Last edited by Novobiocin; 09-06-2012 at 04:21 PM.
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