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  #1  
Old 10-24-2012
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Stats NNT vs NNH

Guys,
According to kaplan i knew that both are kinda similar and depend on inverse of attributable risk (AR).
But today i did one question in UW which states that

NNH- inverse of attributable risk

NNT- inverse of Absolute risk reduction

So can someone clarify more about this?
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Old 10-24-2012
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Attributible risk means that the risk factor increases risk of something as compared to control and is equal to
Exposed event rate - control event rate.
its inverse would be NNH as risk is harmful.

Absolute risk reduction means that exposure to certain factor decreases risk of something as compared to control and is equal
control event rate - exposed event rate
its inverse is NNT as exposure to a certain factor is beneficial.
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Old 10-24-2012
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Question

Quote:
Originally Posted by Timmi View Post
Attributible risk means that the risk factor increases risk of something as compared to control and is equal to
Exposed event rate - control event rate.
its inverse would be NNH as risk is harmful.

Absolute risk reduction means that exposure to certain factor decreases risk of something as compared to control and is equal
control event rate - exposed event rate
its inverse is NNT as exposure to a certain factor is beneficial.

thanks.....

and can you also explain me briefly abt.. recurrence risk reduction...is it the same as absolute risk reduction..?(came across a question in uworld)

and also attributable risk percent too(is it same as attributable risk ?)?

thanks
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Old 10-24-2012
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........................disease.....no disease......
...treated.............50...........40............ .....
....placebo...........20..........30.............. ..


AR=50/90 - 20/50 -------->NNH=1/AR

ARR=20/50 -50/90------->NNT=1/ARR

always align your 2 by 2 table properly & you will get the answer.
hope its clear enough?
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Quote:
Originally Posted by venky2600 View Post
thanks.....

and can you also explain me briefly abt.. recurrence risk reduction...is it the same as absolute risk reduction..?(came across a question in uworld)

and also attributable risk percent too(is it same as attributable risk ?)?

thanks
i dont have concept of these terms. simply had to memorize there formulas after doing U world. And yes both of these terms are different.

Relative risk reduction=( Control event rate-exposed event rate) divided by Control event rate.

attributible risk percent =( Relative risk - 1 ) divided by Relative risk.
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Old 10-24-2012
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Quote:
Originally Posted by Timmi View Post
i dont have concept of these terms. simply had to memorize there formulas after doing U world. And yes both of these terms are different.

Relative risk reduction=( Control event rate-exposed event rate) divided by Control event rate.

attributible risk percent =( Relative risk - 1 ) divided by Relative risk.
thanks

are these true formulas , right..?

i think i messed up with something in my F.A , i annotated that RR-1/RR also for NNT....correct me now..
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Old 10-25-2012
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Quote:
Originally Posted by venky2600 View Post
thanks

are these true formulas , right..?

i think i messed up with something in my F.A , i annotated that RR-1/RR also for NNT....correct me now..
see the following link. Hope it helps.
http://en.wikipedia.org/wiki/Relative_risk_reduction
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Old 10-25-2012
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Quote:
Originally Posted by venky2600 View Post
thanks

are these true formulas , right..?

i think i messed up with something in my F.A , i annotated that RR-1/RR also for NNT....correct me now..
search for relative risk reduction on wikepedia. u ll get ur answer. Extenal links are not allowed i guess,otherwise i wud have posted the link too.
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Old 10-25-2012
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Quote:
Originally Posted by venky2600 View Post
thanks

are these true formulas , right..?

i think i messed up with something in my F.A , i annotated that RR-1/RR also for NNT....correct me now..
venky, RR-1/RR is the formula for atributable risk procent.
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thanks both of you(@teona and @timmi)
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Old 10-28-2012
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Quote:
Originally Posted by Timmi View Post
Attributible risk means that the risk factor increases risk of something as compared to control and is equal to
Exposed event rate - control event rate.
its inverse would be NNH as risk is harmful.

Absolute risk reduction means that exposure to certain factor decreases risk of something as compared to control and is equal
control event rate - exposed event rate
its inverse is NNT as exposure to a certain factor is beneficial.
Ya thats what i concluded from UW but kaplan mentions NNT and NNH as one of same thing. So started this discussion but sorry went missing when the discussion was hot

So home taking tips are:
Attributible risk= exposed rate - control rate
Absolute risk reduction= control rate - exposed
Right?????

And In UW i came across 2 cases

1. find NNT for 2X2 table of drug and placebo VS MI and no MI

2. fint NNH for 2X2 table of drug and placebo VS alive and dead.

So is it just 2 example or is there any specificity in particular examples???
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@koolkillers 88.

according to calculations NNT and NNH are almost the same. For ARR and AR u just need to decide what incidence should be subtracted from what but it doesnt matter in the end e.g
Absoulte risk reduction= control rate- expose rate...even if u reverse it,it doesnt matter in the end except a negative sign that u ignore and it wudnt affect ur calculation of NNT.

in the First example, ideally we need to calculate Absoulte risk reduction first and that wud be
ARR= incidence of MI in patient taking placebo-incidence of MI in patient taking drug.

in the Second example,ideally we need to calculate Attributilble risk first and that would be
AR= incidence of death rate in persons drug-incidence of death in persons taking placebo.


thats the basic concept behind AR,ARR,NNT,NNH. but as i said before it doesnt matter which incidence rate u subtract the other,it wont affect ur calculation except a negative sign that u can ignore.
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