Biostat Question UWSA1 - 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 1 Forum

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


Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 05-19-2014
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 592
Threads: 92
Thanked 195 Times in 127 Posts
Reputation: 205
Send a message via Skype™ to drpisho
Question Biostat Question UWSA1

A new screening test for disease X is positive in 250 out of 1000 affected pts and in 100 out of 1000 healthy control.screening test is applied to population where disease prevalance is 10 000/100,000.how many false positive do u expect per 100,ooo individual in population?

A. 90
b 900
c 1000
d 90,000
d 9000

hi guys, i went with this question and cannot properly do a 2x2 table, please

+DZ ......... -DZ

+.. 2500 ---- 81000
-..750 ----- 9000
10.000........90.000

THE bold part is what i did wrong
when it was turn to do the specificity of the HEALTHY (90.000 x 0.1) it came 9000 which according to what ive studied specificity corresponds to the TRUE NEGATIVE population (true negative rate, stated in FA), that is why i putted them on the truly negative, however i seem to be doing something wrong. im really weak in this,
please some kind soul help me why is it 9000 that is the FALSE POSITIVE

thanks in advance.
__________________
Will. Power. Faith. MATCHED IM 2016!

Last edited by drpisho; 05-19-2014 at 06:24 AM.
Reply With Quote Quick reply to this message



  #2  
Old 05-19-2014
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 592
Threads: 92
Thanked 195 Times in 127 Posts
Reputation: 205
Send a message via Skype™ to drpisho
Default

i got it,!!!
sad that no one helped me here, but anyways finally understood it.

ignore this thread lol.
__________________
Will. Power. Faith. MATCHED IM 2016!
Reply With Quote Quick reply to this message
  #3  
Old 05-19-2014
excellence's Avatar
USMLE Forums Addict
 
Steps History: 1 + CK
Posts: 143
Threads: 12
Thanked 59 Times in 38 Posts
Reputation: 69
Default

i got it too...& i want to share it...

A new screening test for disease X is positive in 250 out of 1000 affected pts and in 100 out of 1000 healthy control.screening test is applied to population where disease prevalance is 10 000/100,000.how many false positive do u expect per 100,ooo individual in population?

as the q asking for FP=?
we only need to calculate specificity: 100 out of 1000 healthy --> specificty = 90% & FP=10%

disease prevalance is 10 000/100,000 --> healthy people= 90,000

so FP= 10% of 90,000= 9000
Reply With Quote Quick reply to this message
The above post was thanked by:
drpisho (05-19-2014), Meli (05-20-2014), placebo (05-19-2014)



Reply

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
BioStat Question for Today drpisho USMLE Step 1 Forum 7 04-01-2016 03:01 AM
BioStat Question for Today - 2 drpisho USMLE Step 1 Forum 3 04-29-2014 01:22 PM
BioStat Question for Today drpisho USMLE Step 1 Forum 5 04-28-2014 03:14 PM
biostat confidence interval question? dr.dhruvdesai USMLE Step 1 Forum 5 07-18-2011 12:25 PM
biostat Hardy weinberg question dr.dhruvdesai USMLE Step 1 Forum 3 07-18-2011 03:23 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)