Positive Predictive Value from Specificity and Sensitivity! - 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 10-31-2012
tyagee's Avatar
USMLE Forums Master
 
Steps History: ---
Posts: 1,365
Threads: 648
Thanked 588 Times in 354 Posts
Reputation: 598
Stats Positive Predictive Value from Specificity and Sensitivity!

Several tests have been developed to measure serologic markers of breast cancer. The sensitivity and specificity for
diagnosis of early stage breast cancer vary from test to test. If positive, which of the following tests will have the
highest predictive value for the disease?
o A) Sensitivity - 80%, specificity- 90%
0 B) Sensitivity - 65%, specificity - 97%
o C) Sensitivity - 70%, specificity - 94%
0 D) Sensitivity - 75%, specificity - 92%
0 E) Sensitivity - 85%, specificity - 90%
Reply With Quote Quick reply to this message



  #2  
Old 11-01-2012
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

Specificity = probability that a person without the disease will test negative. In other words, the more specific the test, the more chances are that the person has the disease. So answer should be B.
Reply With Quote Quick reply to this message
The above post was thanked by:
tyagee (11-01-2012)
  #3  
Old 11-01-2012
USMLE Forums Master
 
Steps History: 1+CK+CS
Posts: 720
Threads: 217
Thanked 552 Times in 309 Posts
Reputation: 562
Default

N for N --- seNsitivity related to Negative predictive value..

P for P ---- sPecificity related to Positive predictive value


Reply With Quote Quick reply to this message
The above post was thanked by:
Novobiocin (11-01-2012)
 
  #4  
Old 11-01-2012
nooranimm's Avatar
USMLE Forums Scout
 
Steps History: Not yet
Posts: 75
Threads: 3
Thanked 35 Times in 23 Posts
Reputation: 45
Default

So if u r trying to catch breast cancer earlier, you will need a test that will be make u confident enough that the lady who tests positive indeed has the test. So option B is the most likely one
Reply With Quote Quick reply to this message
The above post was thanked by:
tyagee (11-01-2012)
  #5  
Old 11-01-2012
tyagee's Avatar
USMLE Forums Master
 
Steps History: ---
Posts: 1,365
Threads: 648
Thanked 588 Times in 354 Posts
Reputation: 598
Default

Quote:
Originally Posted by cingulate.gyrus View Post
N for N --- seNsitivity related to Negative predictive value..

P for P ---- sPecificity related to Positive predictive value


hey cingulate, this vertical line to left in graph.... doesnt it denotes Sn ?
Reply With Quote Quick reply to this message
  #6  
Old 11-01-2012
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

B, the greatest value of specificity is the one you are looking for

Specificity rules IN

Sensitivity rules OUT

IN order to rule in you have to have an excellent PPV.
In order to rule out you have to have an excellent NPV

So that if a specific test comes back positive then you have the disease no matter what.
Reply With Quote Quick reply to this message
The above post was thanked by:
Novobiocin (11-01-2012)
  #7  
Old 11-01-2012
USMLE Forums Master
 
Steps History: 1+CK+CS
Posts: 720
Threads: 217
Thanked 552 Times in 309 Posts
Reputation: 562
Default

Quote:
Originally Posted by tyagee View Post
hey cingulate, this vertical line to left in graph.... doesnt it denotes Sn ?

The right of vertical line is sensitivity( All the diseased case).
And the left of which is negative predictive value(Non of the diseased case)

similarly a life can be drawn in other side which divide graph to specificity and positive predictive value..

Its beautifully described in Kaplan vedios... watch it...Difficult to expain.
Reply With Quote Quick reply to this message
The above post was thanked by:
Novobiocin (11-01-2012), tyagee (11-01-2012)
  #8  
Old 11-01-2012
USMLE Forums Master
 
Steps History: 1+CK+CS
Posts: 1,867
Threads: 149
Thanked 2,104 Times in 1,049 Posts
Reputation: 2124
Default

Quote:
Originally Posted by cingulate.gyrus View Post
Its beautifully described in Kaplan videos...
Especially the part where Dr.Daugherty said only to look at the bottom of the graph and ignore the top.
__________________
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
The above post was thanked by:
tyagee (11-01-2012)



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
Sensitivity, Specificity, PPV, NPV Renaissance USMLE Step 1 Forum 3 07-07-2012 07:46 AM
Specificity Sensitivity Question! tyagee USMLE Step 1 Forum 3 03-09-2012 06:48 AM
parameters of sensitivity and specificity manphnx USMLE Step 1 Forum 6 01-31-2011 12:35 AM
Positive Predictive Value Versus Sensitivity schiwei USMLE Step 1 Forum 1 12-04-2010 08:58 AM
What is the effect of the cut-off value on sensitivity/specificity/predictive values? zein1 USMLE Step 1 Forum 2 11-12-2010 04:28 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)