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#1
12-08-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 623 Threads: 111 Thanked 424 Times in 264 Posts Reputation: 434
Absolute Risk Reduction and Number Needed to Treat?

In a study,
100 patients received medication X to prevent the development of diabetes and 200 patients did not receive the medication, 10 patients in the experimental group and 40 patients patients in the control group developed diabetes, what is the absolute risk reduction and number needed to treat?

#2
12-08-2011
 USMLE Forums Newbie Steps History: Step 1 Only Posts: 5 Threads: 0 Thanked 3 Times in 1 Post Reputation: 13

Quote:
 Originally Posted by aknz In a study, 100 patients received medication X to prevent the development of diabetes and 200 patients did not receive the medication, 10 patients in the experimental group and 40 patients patients in the control group developed diabetes, what is the absolute risk reduction and number needed to treat?
10/100= 0.1
40/200= 0.2
ARR= 0.2-0.1= 0.1
NNT= 1/ 0.1= 10

 The above post was thanked by: aknz (12-08-2011), curiousmind (07-18-2012), mmtj (05-11-2012)
#3
12-08-2011
 USMLE Forums Guru Steps History: 1 + CS Posts: 300 Threads: 22 Thanked 97 Times in 62 Posts Reputation: 107

10% and 10 is the number needed to treat
 The above post was thanked by: mmtj (05-11-2012)

#4
12-08-2011
 USMLE Forums Scout Steps History: 1+CK+CS Posts: 51 Threads: 7 Thanked 79 Times in 32 Posts Reputation: 89
Abste risk reduction

absolute risk reduction = 10/100 - 40/200 = -10/100
I.e. 10 patients for every 100 patients will not have the disease compared to placebo
NNT= 100/10 = 10 patients i.e. Fir every 10 patients receiving the drug 1 will have benefit

Last edited by alaahoda2001; 12-08-2011 at 04:25 PM.
#5
12-08-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 623 Threads: 111 Thanked 424 Times in 264 Posts Reputation: 434

Quote:
 Originally Posted by vin31md 10/100= 0.1 40/200= 0.2 ARR= 0.2-0.1= 0.1 NNT= 1/ 0.1= 10
#6
07-18-2012
 USMLE Forums Scout Steps History: Not yet Posts: 46 Threads: 6 Thanked 21 Times in 11 Posts Reputation: 31

Thank u guys that was nice discussion.

Can anybody tell me what's the relative risk reduction here? For the same question?
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#7
07-19-2012
 USMLE Forums Scout Steps History: 1 + CS Posts: 90 Threads: 23 Thanked 14 Times in 9 Posts Reputation: 24

Vin31md: Nicely done but calculation is wrong...the answer should be negative to make sure ur doin it right...
its risk reduction...... -0.1 --> -10% reduction

a/(a+b) / c/(c+d) ---> 0.1 - 0.2 = -0.1
#8
06-11-2013
 USMLE Forums Scout Steps History: 1 + CS Posts: 95 Threads: 7 Thanked 67 Times in 21 Posts Reputation: 87

Quote:
 Originally Posted by phantom86 Vin31md: Nicely done but calculation is wrong...the answer should be negative to make sure ur doin it right... its risk reduction...... -0.1 --> -10% reduction a/(a+b) / c/(c+d) ---> 0.1 - 0.2 = -0.1

The initial question asked Number Needed To Treat ( NNT ) .
For NNT formula is : NNT= 1/Absolute Risk Reduction = 1/ARR = 1/(c/d)-(a/b) .

For Numbers Needed to Harm
The formula becomes :
NNH = 1/Atributable risk = 1/a/(a+b)-c/(c+ d)
#9
06-11-2013
 USMLE Forums Scout Steps History: Not yet Posts: 27 Threads: 1 Thanked 9 Times in 7 Posts Reputation: 19

Quote:
 Originally Posted by aknz In a study, 100 patients received medication X to prevent the development of diabetes and 200 patients did not receive the medication, 10 patients in the experimental group and 40 patients patients in the control group developed diabetes, what is the absolute risk reduction and number needed to treat?
NNT= 1/ARR

ARR= Control Event rate - experimental event rate
ARR =40/200-10/100=0.2-0.1=0.1

NNT=1/0.1=10

10 people need to be treated to prevent one diabetes case development

 Tags Biostatistics-Epidemiology, Step-1-Questions

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