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#1
07-11-2012
 USMLE Forums Master Steps History: --- Posts: 1,365 Threads: 648 Thanked 591 Times in 355 Posts Reputation: 601
Number Needed to Treat (NNT)!

A study is done to test a new treatment for heart failure. Patients received usual CHF treatment plus Drug X or usual treatment plus placebo. 10/50 patients who received the drug died, and 20/50 patients who received the placebo died.
What is the number needed to treat (NNT) for this new drug?

A. 2
B. 5
C. 10
D. 15
E. 50

btw, how much high yield is this for ck ? NNT concept....
 The above post was thanked by: mmtj (07-17-2012)

#2
07-11-2012
 USMLE Forums Addict Steps History: Step 1 Only Posts: 127 Threads: 3 Thanked 113 Times in 62 Posts Reputation: 123

B.

For every 50 patients that you treated, you had an improved outcome in 10 patients. So, if you just divide through by 10, then for every 5 patients that you treat, you have 1 improved outcome. That's basically the concept of NNT.

As far as how high-yield it is... it's a fairly simple concept, so even if there's a relatively small chance that you'll get a question on it, you should know what it is.

Also, you should know the absolute risk reduction (ARR), which is the inverse of the NNT. You reduced the risk in 10 patients for every 50 patients who you treated, so your absolute risk reduction is 10/50=1/5, and your NNT = 1/ARR = 1/(1/5) = 5.
 The above post was thanked by: Novobiocin (07-12-2012), oti nogonno (07-12-2012), sonu.agarwall (07-12-2012)
#3
07-11-2012
 USMLE Forums Master Steps History: --- Posts: 1,365 Threads: 648 Thanked 591 Times in 355 Posts Reputation: 601

Quote:
 Originally Posted by shan564 B. For every 50 patients that you treated, you had an improved outcome in 10 patients. So, if you just divide through by 10, then for every 5 patients that you treat, you have 1 improved outcome. That's basically the concept of NNT. As far as how high-yield it is... it's a fairly simple concept, so even if there's a relatively small chance that you'll get a question on it, you should know what it is. Also, you should know the absolute risk reduction (ARR), which is the inverse of the NNT. You reduced the risk in 10 patients for every 50 patients who you treated, so your absolute risk reduction is 10/50=1/5, and your NNT = 1/ARR = 1/(1/5) = 5.
thanks for such a clear explanation.

i also remember that NNT is inverse of incidence. now ARR is also inverse of NNT . stats !:sorry:

#4
07-12-2012
 USMLE Forums Addict Steps History: Step 1 Only Posts: 127 Threads: 3 Thanked 113 Times in 62 Posts Reputation: 123

Quote:
 Originally Posted by tyagee i also remember that NNT is inverse of incidence.
Not sure what you mean by that - maybe only in a specific context. Incidence and NNT can't be related to each other directly, since incidence is a measure of burden of disease, while NNT is a measure of treatment efficacy.
 The above post was thanked by: tyagee (07-12-2012)
#5
07-12-2012
 USMLE Forums Addict Steps History: 1+CK+CS Posts: 185 Threads: 42 Thanked 108 Times in 61 Posts Reputation: 118

In easy way NNT is inverse of absolute risk reduction.

No of patients with the risk factor - no of patients without the risk factor=ARR

& NNT = 1/ARR!!!

hope that it will help.

This concept is really very imp for CK....HY!!!!
 The above post was thanked by: tyagee (07-12-2012)
#6
07-12-2012
 USMLE Forums Veteran Steps History: 1+CK+CS Posts: 289 Threads: 7 Thanked 129 Times in 102 Posts Reputation: 139
B

Would go with B.

The NNT is the inverse of the risk reduction ratio so:
Risk reduction ratio is : 20/50 - 10/50 = 0.2

NNT= 1/0.2= 5
#7
07-12-2012
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yes i would go with B)5
#8
07-12-2012
 USMLE Forums Master Steps History: --- Posts: 1,365 Threads: 648 Thanked 591 Times in 355 Posts Reputation: 601

ans is indeed B !

what will be NNH number needed to harm in this question ?

Last edited by tyagee; 07-12-2012 at 01:24 PM.
#9
07-12-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,867 Threads: 149 Thanked 2,107 Times in 1,049 Posts Reputation: 2127

Quote:
 Originally Posted by tyagee what will be NNH number needed to harm in this question ?
It is same as Number needed to treat.
#10
07-12-2012
 USMLE Forums Veteran Steps History: 1+CK+CS+3 Posts: 205 Threads: 6 Thanked 151 Times in 80 Posts Reputation: 161

Quote:
 Originally Posted by tyagee A study is done to test a new treatment for heart failure. Patients received usual CHF treatment plus Drug X or usual treatment plus placebo. 10/50 patients who received the drug died, and 20/50 patients who received the placebo died. What is the number needed to treat (NNT) for this new drug? A. 2 B. 5 C. 10 D. 15 E. 50 btw, how much high yield is this for ck ? NNT concept....
Just to add few details to those people who are new to this concept here is how it should be worked out:

First find absolute risk reduction=Incidence in control group-Incidence in drug group ie 20/50-10/50=0.2 or 22% means that 22% of patients were saved from Heart faillure by using the drug X

Now we already know that Number needed to treat= 100/absolute risk reduction
plugging value from above 100/20=5 means that 5 patients would have to be treated to save one life so answer is B
#11
07-17-2012
 USMLE Forums Scout Steps History: Not yet Posts: 46 Threads: 6 Thanked 21 Times in 11 Posts Reputation: 31

Quote:
 Originally Posted by shan564 B. For every 50 patients that you treated, you had an improved outcome in 10 patients. So, if you just divide through by 10, then for every 5 patients that you treat, you have 1 improved outcome. That's basically the concept of NNT. As far as how high-yield it is... it's a fairly simple concept, so even if there's a relatively small chance that you'll get a question on it, you should know what it is. Also, you should know the absolute risk reduction (ARR), which is the inverse of the NNT. You reduced the risk in 10 patients for every 50 patients who you treated, so your absolute risk reduction is 10/50=1/5, and your NNT = 1/ARR = 1/(1/5) = 5.

I'm not sure of what you meant by that, but you have 10 patients died after treatment with the drug X, and that's not improve the outcome.
would you clarify for me please

you have 40 people lived after drug X compared to 30 people compared to placebo, and that's an improvement, isn't it?

so simple the table will be like this:

drug placebo
Alive 40 30

so ARR is 40/50-30/50 and that equals 1/5. NNT= 5

anyone would correct me if I was wrong please, and also if you guys help extract NNH, that would be awesome.
#12
07-17-2012
 USMLE Forums Scout Steps History: Not yet Posts: 46 Threads: 6 Thanked 21 Times in 11 Posts Reputation: 31

I DON'T KNOW WHY THE TABLE IS LIKE THAT BUT I THINK IT'S UNDERSTANDABLE
#13
07-17-2012
 USMLE Forums Scout Steps History: Not yet Posts: 46 Threads: 6 Thanked 21 Times in 11 Posts Reputation: 31

That would be number 3 I believe .
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#14
07-18-2012
 USMLE Forums Scout Steps History: Not yet Posts: 46 Threads: 6 Thanked 21 Times in 11 Posts Reputation: 31

Quote:
 Originally Posted by USMLEbiostats.co I woke-up this morning understanding my flub/mistake but, it happens that, #2 is correct (I really hope I'm helping more than hurting!). NNT=5 so, Of every 5 patients treated, 1 patient will benefit or, also true is Of every 50 patients treated, 10 patient will benefit (multiply eveything by 10). HOWEVER, i doubt that answers get tricky like #2 (multiply by 10). I believe the concept would be asked and answered like #1: If NNT=5, then 1 patient benefits for evey 5 treated. LANGUAGE: The answer could also be written as (NNT=5): Of every 5 patients treated, 1 patient will avoid a bad outcome. Sorry -- the wife is an IMG. i'm just the side-kick....
haha, yeah you got me on that one, it's one person per five. lol nice one and thanks for clarifying.
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An Intellectual is someone who's mind watches itself.

 Tags Biostatistics-Epidemiology, Step-2-Questions

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