Biostatistics Q.. - USMLE Forums
 USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
 Home USMLE Articles USMLE News USMLE Polls USMLE Books USMLE Apps
 USMLE Forums Biostatistics Q..

 USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam

#1
08-29-2012
 USMLE Forums Guru Steps History: 1+CK+CS+3 Posts: 304 Threads: 48 Thanked 320 Times in 113 Posts Reputation: 330
Biostatistics Q..

You are asked to evaluate the efficacy of new lipid lowering drug marked as "superstatin" results of randomized control trial at 5yrs are given at the table below
Treatment with Superstatin Treatment with Placebo
M.Infarction 10 25
No M Infarction 990 975

what is the number needed to treat to prevent one myocardial infarction with superstatin.

p:s i can't post the answer options because i wanna know how it's solved. Thanks!!!.... i'll post when it's done.

#2
08-29-2012
 USMLE Forums Master Steps History: Step 1 Only Posts: 864 Threads: 62 Thanked 406 Times in 247 Posts Reputation: 416
66.6

Attributable risk- 25/1000-10/1000= 15/1000

No needed to treat= 1000/15=66.6
__________________
One day i will infect these microbes and they will search for "Anti-MEbiotic"....
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
 The above post was thanked by: dockhi (08-30-2012), obinocle (08-29-2012)
#3
08-30-2012
 USMLE Forums Scout Steps History: Not yet Posts: 96 Threads: 15 Thanked 19 Times in 18 Posts Reputation: 29

is that the correct asnwer?
isnt the forumla a/ a+b - c/c+d

#4
08-30-2012
 USMLE Forums Guru Steps History: 1+CK+CS+3 Posts: 304 Threads: 48 Thanked 320 Times in 113 Posts Reputation: 330

Quote:
 Originally Posted by pathophysio1 is that the correct asnwer? isnt the forumla a/ a+b - c/c+d
Yea pathphisio thatz the correct answer..
#5
08-30-2012
 USMLE Forums Guru Steps History: 1+CK+CS Posts: 307 Threads: 36 Thanked 132 Times in 65 Posts Reputation: 142

koolkiller,
In the 2x2 table, we're supposed to take 'a' as Diseased and Exposed right? So in this question, the 'a' cell is going to be patients with MI & who took placebo? Didn't understand how to arrive at that. Would appreciate your help, thanks!
#6
08-30-2012
 USMLE Forums Scout Steps History: Not yet Posts: 96 Threads: 15 Thanked 19 Times in 18 Posts Reputation: 29

NNT = 1/ARR= numbb. of people who were treated with the drug and had a MI subtracted by the number of ppl who had a MI taking placebo that = ARR and then do 1 /ARR
#7
08-30-2012
 USMLE Forums Master Steps History: Step 1 Only Posts: 864 Threads: 62 Thanked 406 Times in 247 Posts Reputation: 416
Hope it help

Quote:
 Originally Posted by dockhi koolkiller, In the 2x2 table, we're supposed to take 'a' as Diseased and Exposed right? So in this question, the 'a' cell is going to be patients with MI & who took placebo? Didn't understand how to arrive at that. Would appreciate your help, thanks!
I always get confused by this a and b stuff. So i just do my calculations according to question.
Attributable risk- Incidence rate of exposed group minus incidence rate of non exposed group.
So exposed group will be those who are on superstatin.
In this question, if we make 2X2 table,
then,
Superstatin placebo
MI 25 10
non MI 975 990
__________________
One day i will infect these microbes and they will search for "Anti-MEbiotic"....
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
#8
08-31-2012
 USMLE Forums Guru Steps History: 1+CK+CS Posts: 307 Threads: 36 Thanked 132 Times in 65 Posts Reputation: 142

Quote:
 Originally Posted by koolkiller88 I always get confused by this a and b stuff. So i just do my calculations according to question. Attributable risk- Incidence rate of exposed group minus incidence rate of non exposed group. So exposed group will be those who are on superstatin. In this question, if we make 2X2 table, then, Superstatin placebo MI 25 10 non MI 975 990
Alright, makes sense.. But doesn't the question state that 10 people had MI when they were on Superstatin,and 25 people had MI when they were on placebo? Sorry to sound dumb here, but really appreciate the help!
#9
08-31-2012
 USMLE Forums Master Steps History: Step 1 Only Posts: 864 Threads: 62 Thanked 406 Times in 247 Posts Reputation: 416

Quote:
 Originally Posted by dockhi Alright, makes sense.. But doesn't the question state that 10 people had MI when they were on Superstatin,and 25 people had MI when they were on placebo? Sorry to sound dumb here, but really appreciate the help!
Ya true, Just took a proper look. Ok you can change it. I am never good at 2X2 tables.
__________________
One day i will infect these microbes and they will search for "Anti-MEbiotic"....
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
#10
08-31-2012
 USMLE Forums Guru Steps History: 1+CK+CS Posts: 307 Threads: 36 Thanked 132 Times in 65 Posts Reputation: 142

Quote:
 Originally Posted by koolkiller88 Ya true, Just took a proper look. Ok you can change it. I am never good at 2X2 tables.
Regardless, you taught me how to USE the formula. Thank you! Btw, when are you taking the Exam? I'm scheduled for October. Feel lousy!!
#11
08-31-2012
 USMLE Forums Master Steps History: Step 1 Only Posts: 864 Threads: 62 Thanked 406 Times in 247 Posts Reputation: 416

Quote:
 Originally Posted by dockhi Regardless, you taught me how to USE the formula. Thank you! Btw, when are you taking the Exam? I'm scheduled for October. Feel lousy!!
I scheduled for Nov. YA "lousy feeling" is a common thing will all share.
__________________
One day i will infect these microbes and they will search for "Anti-MEbiotic"....
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

 Tags Biostatistics-Epidemiology

Message:
Options

## Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
User Name:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
 AMG IMG ---
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.

 Not yet Step 1 Only CK Only CS Only 1 + CK 1 + CS 1+CK+CS CK+CS 1+CK+CS+3 ---
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

 Similar Threads Thread Thread Starter Forum Replies Last Post aj23 USMLE Step 1 Forum 0 06-30-2012 11:54 PM rose USMLE Step 1 Forum 0 01-19-2012 01:25 PM rsin21 USMLE Step 1 Forum 1 11-15-2011 06:08 AM bebix USMLE Step 1 Forum 7 06-02-2011 08:56 AM Doctor Queen USMLE Step 1 Forum 2 10-17-2010 10:43 PM