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#1




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 ? 
#2




Number needed to treat(NNT) in this case prevent deaths=1/ARR=50%

#3




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 ... ??

#4




Quote:
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. 
The above post was thanked by:  
Awwad (03172013) 
#5




To be correct answer you should divide by 80/160, so the correct answer is 50%, not 25%.

#6




Quote:
Number needed to treat(NNT)=1/ARR=4 
#7




25 %................................................. ....

#8




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. 
#9




RRR
Quote:
RRR= ARR/Control Group .25/.5= .5 = 50 percent RRR Correct me if im wrong 
#10




Quote:
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 
The above post was thanked by:  
Oscaryasser (11232013) 
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BiostatisticsEpidemiology 
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