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#1




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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#2




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. 
#3




Quote:
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 


#4




........................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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#5




Quote:
Relative risk reduction=( Control event rateexposed event rate) divided by Control event rate. attributible risk percent =( Relative risk  1 ) divided by Relative risk. 
#6




Quote:
are these true formulas , right..? i think i messed up with something in my F.A , i annotated that RR1/RR also for NNT....correct me now.. 
#7




Quote:
http://en.wikipedia.org/wiki/Relative_risk_reduction 
#8




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.

The above post was thanked by:  
venky2600 (10252012) 
#10




thanks both of you(@teona and @timmi)

#11




Quote:
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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#12




@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 placeboincidence 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 drugincidence 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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koolkiller88 (10282012) 
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BiostatisticsEpidemiology 
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