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  #1  
Old 01-19-2013
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Stats Absolute risk reduction versus Relative risk reduction

160 people in placebo , 80 died .
200 people in Drug X , 50 died .
what % of deaths were prevented by DRug X ?
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Old 01-20-2013
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Number needed to treat(NNT) in this case prevent deaths=1/ARR=50%
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Old 01-20-2013
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Quote:
Originally Posted by doc.mav View Post
Number needed to treat(NNT) in this case prevent deaths=1/ARR=50%
doc .mav could you please explain how you got 50% ....i really get confused with this NNT ....ARR for this case is 25% ..is it right ... ??
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Old 01-20-2013
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Quote:
Originally Posted by doc.mav View Post
Number needed to treat(NNT) in this case prevent deaths=1/ARR=50%


NNT would not be given in a percentage.


This question is just asking attributable risk reduction.
(80/160)-(50/200)= 25%
With the drug we have prevented 25% of the fatal cases from occurring.
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  #5  
Old 11-11-2013
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Quote:
Originally Posted by SOBE223 View Post
NNT would not be given in a percentage.


This question is just asking attributable risk reduction.
(80/160)-(50/200)= 25%
With the drug we have prevented 25% of the fatal cases from occurring.
To be correct answer you should divide by 80/160, so the correct answer is 50%, not 25%.
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Old 11-12-2013
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Quote:
Originally Posted by ag2011n View Post
To be correct answer you should divide by 80/160, so the correct answer is 50%, not 25%.
ARR=(80/160)-(50/200)=(1/2)-(1/4)=1/4=25%
Number needed to treat(NNT)=1/ARR=4
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Old 11-12-2013
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25 %................................................. ....
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Old 11-22-2013
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absolute risk reduction= subtract the risk ratio of drugX from risk ratio of placebo.

ARR= 80/160 - 50/200 = 0.5 - 0.25 = 0.25 = 25%

so, drug X reduced the absolute risk of death by 25% in the population


relative risk reduction = divide the risk ratio of placebo group with risk ratio of drugX

RRR= 50/200 / 80/160 = 0.5/0.25 = 2

so, relative risk of death with drug X is 2 times less likely than in the placebo group. Or
in other words, placebo group has 2 times more risk of death than the drug X.
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  #9  
Old 11-22-2013
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Default RRR

Quote:
Originally Posted by organo14 View Post
absolute risk reduction= subtract the risk ratio of drugX from risk ratio of placebo.

ARR= 80/160 - 50/200 = 0.5 - 0.25 = 0.25 = 25%

so, drug X reduced the absolute risk of death by 25% in the population


relative risk reduction = divide the risk ratio of placebo group with risk ratio of drugX

RRR= 50/200 / 80/160 = 0.5/0.25 = 2

so, relative risk of death with drug X is 2 times less likely than in the placebo group. Or
in other words, placebo group has 2 times more risk of death than the drug X.

RRR= ARR/Control Group .25/.5= .5 = 50 percent RRR
Correct me if im wrong
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Old 11-23-2013
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Quote:
Originally Posted by Oscaryasser View Post
RRR= ARR/Control Group .25/.5= .5 = 50 percent RRR
Correct me if im wrong
well, i used the formula of relative risk, which tells not only the increased risk in a group but also a reduced risk in the other group, depending upon what is being asked.

so, i used the formula telling that placebo group has 2 times more chances of deaths than in the drugX group.

so, i can aslo reframe it as, drugX has 2 times less chances of deaths than in placebo group.
' 2 times less' means one half chances (0.5),
so drugX has 0.5 chances of deaths than in placebo group ( as you calculated).


the only diference is in the method, you directly put it and i indirectly.

your way is very useful if we knew the ARR. i hadn't come across it.

thankyou
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