Calculating the Number Needed to Treat? - USMLE Forums
USMLE Forums Logo
USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
Home
USMLE Articles
USMLE News
USMLE Polls
USMLE Books
USMLE Apps
Go Back   USMLE Forums > USMLE Step 2 CK Forum

USMLE Step 2 CK Forum USMLE Step 2 CK Discussion Forum: Let's talk about anything related to USMLE Step 2 CK exam


Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 10-24-2012
USMLE Forums Veteran
 
Steps History: Not yet
Posts: 234
Threads: 120
Thanked 11 Times in 10 Posts
Reputation: 21
Calculator Calculating the Number Needed to Treat?

several pts with HTN whom you have treated for years have recently had strokes. you conduct a trial which shows that a partictuar anti htn lowers risk from 8 per 1000 pts to 6 per 1000 pts with relative risk reduction of 25%. wat is the number need to treat?

a. 4
b. 250
c. 500
d. 1000
e. 750
please explain
Reply With Quote Quick reply to this message



  #2  
Old 10-24-2012
XpaezX's Avatar
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 1,216
Threads: 41
Thanked 1,327 Times in 711 Posts
Reputation: 1342
Default

C) 500

NNT is 1/ARR or 1/(8/1000-6/1000)

1/(.008-.006)
1/.002 = 500

You just have to divide 8 /1000 and 6/1000 substract and that result divided by 1 and you get the answer

If they give you Absolute risk reduction in the question stem then is even easier because you just divide 1/ ARR
Reply With Quote Quick reply to this message
The above post was thanked by:
eriqaly (08-17-2015), Novobiocin (10-24-2012)
  #3  
Old 10-24-2012
USMLE Forums Addict
 
Steps History: Step 1 Only
Posts: 136
Threads: 18
Thanked 84 Times in 37 Posts
Reputation: 94
Default

xpaezx has correctly mentioned ...

the other Technic is that,,,

To save 2 more people(with anti htn drug; 8-6=2), I need to treat 1000 patients; so how many patients will i have to treat to save 1 ?????

its simple in this question: 500..(1 * 1000 divided by 2)

in other questions,,yu can put it same way..

for eg,,,10 out of 1000 patient survive without Rx in certain disease, and 30 out of 500 survive with Rx with drug X..calculate the number needed to treat..

In this case, first we will have to equalize the number in both groups as number of patients in both the groups differ(500 & 1000)..we can consider that 60 out 1000 survive in Rx group (instead of 30 out of 500)....

Now, to save 50 more patients(60-10=50) , we need to treat 1000...so to save 1 patient we need to treat how many???

its 1*1000 divided by 50 = 20 patients...

It may seem confusing, but once this concept is understood, its really a faster way to calculate number needed to treat questions; without calculating Relative risk and absolute risk reduction...
Reply With Quote Quick reply to this message
The above post was thanked by:
eriqaly (08-17-2015), Imgfrmhalifax (10-24-2012), luschka (02-19-2013), Novobiocin (10-24-2012), Syndrome X (10-24-2012), vaibhavmanu (10-24-2012)
 
  #4  
Old 10-24-2012
vaibhavmanu's Avatar
USMLE Forums Guru
 
Steps History: 1+CK+CS+3
Posts: 385
Threads: 6
Thanked 205 Times in 154 Posts
Reputation: 215
Default

Thanks buddy. That was a nice way to deal with this problem!
Reply With Quote Quick reply to this message
  #5  
Old 10-24-2012
USMLE Forums Master
 
Steps History: 1+CK+CS
Posts: 1,867
Threads: 149
Thanked 2,106 Times in 1,049 Posts
Reputation: 2126
Default

Great explanations.

How do you calculate NNH ?
__________________
A man doesn't know what he knows until he knows what he doesn't know.
“What is man? He's just a collection of chemicals with delusions of grandeur.”
Reply With Quote Quick reply to this message
  #6  
Old 10-24-2012
XpaezX's Avatar
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 1,216
Threads: 41
Thanked 1,327 Times in 711 Posts
Reputation: 1342
Default

Quote:
Originally Posted by Novobiocin View Post
Great explanations.

How do you calculate NNH ?

I would like to assume is the same? but the question must ask that instead of NNT? and must imply in the vignette how many people were harmed and the like
Reply With Quote Quick reply to this message



Reply

Tags
Biostatistics-Epidemiology, Step-2-Questions

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
USMLE Steps History
What steps finished! Example: 1+CK+CS+3 = Passed Step 1, Step 2 CK, Step 2 CS, and Step 3.

Choose "---" if you don't want to tell.

Favorite USMLE Books
What USMLE books you really think are useful. Leave blank if you don't want to tell.
Location
Where you live. Leave blank if you don't want to tell.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Absolute Risk Reduction and Number Needed to Treat? aknz USMLE Step 1 Forum 8 06-11-2013 05:59 PM
Number Needed to Treat (NNT)! tyagee USMLE Step 2 CK Forum 13 07-18-2012 08:48 AM
Number Needed To Treat Calculation? qurat21 USMLE Step 1 Forum 4 12-18-2011 02:58 AM
Number needed to treat and number needed to harm kemoo USMLE Step 2 CK Forum 2 06-17-2011 11:41 PM
Number Needed to Treat kalpana USMLE Step 1 Forum 2 12-21-2009 11:14 AM

RSS Feed
Find Us on Facebook
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

USMLE® & other trade marks belong to their respective owners, read full disclaimer
USMLE Forums created under Creative Commons 3.0 License. (2009-2014)