Confounding bias versus Effects Modification - 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 05-15-2011
USMLE Forums Scout
 
Steps History: 1 + CK
Posts: 91
Threads: 17
Thanked 108 Times in 37 Posts
Reputation: 118
Stats Confounding bias versus Effects Modification

Hi everybody

Can you please explain the difference between confounding bias and effect modification! I didn't get the explanation from UW

thank you
Reply With Quote Quick reply to this message



  #2  
Old 05-15-2011
bebix's Avatar
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 1,357
Threads: 194
Thanked 3,259 Times in 881 Posts
Reputation: 3269
Default

This is a pretty short (2 pages) article explaining the diff. between them:
http://courses.washington.edu/b570/h...onfounding.pdf

and here you´ll find a lot of examples (Stanford U)
www.stanford.edu/~kcobb/hrp261/lecture2.ppt
Reply With Quote Quick reply to this message
The above post was thanked by:
tinhi (05-15-2011)
  #3  
Old 05-15-2011
USMLE Forums Guru
 
Steps History: ---
Posts: 332
Threads: 48
Thanked 168 Times in 107 Posts
Default

Confounding factor is a specific variable that is associated with both the effect and the outcome. Example---When studying the effects of smoking and esophageal cancer, ALCOHOLISM is a confounding factor since patients who smoke tends to drink and drinking is a risk factor of esophageal cancer.

Effect modification is when effect of exposure on disease differs in strata groups of the population. e.g. tetracycline causes discoloration in children but not in adult.
Reply With Quote Quick reply to this message
The above post was thanked by:
Candy Girl (05-16-2011), dinosaur108 (09-01-2011), israaoday (10-26-2014), tinhi (05-15-2011), vaibhavmanu (05-17-2011)
  #4  
Old 05-15-2011
USMLE Forums Scout
 
Steps History: 1 + CK
Posts: 91
Threads: 17
Thanked 108 Times in 37 Posts
Reputation: 118
Default

Quote:
Originally Posted by usluipek View Post
Confounding factor is a specific variable that is associated with both the effect and the outcome. Example---When studying the effects of smoking and esophageal cancer, ALCOHOLISM is a confounding factor since patients who smoke tends to drink and drinking is a risk factor of esophageal cancer.

Effect modification is when effect of exposure on disease differs in strata groups of the population. e.g. tetracycline causes discoloration in children but not in adult.
Quote:
Originally Posted by bebix View Post
This is a pretty short (2 pages) article explaining the diff. between them:
http://courses.washington.edu/b570/h...onfounding.pdf

and here you´ll find a lot of examples (Stanford U)
www.stanford.edu/~kcobb/hrp261/lecture2.ppt
Thank you so much for the replay and the great explanation; things are more clear now
Reply With Quote Quick reply to this message
  #5  
Old 06-13-2011
USMLE Forums Guru
 
Steps History: Not yet
Posts: 324
Threads: 70
Thanked 236 Times in 143 Posts
Reputation: 246
Question How to differentiate between confounding and effect modification?

How to differentiate between Confounding and Effect modification?..
They both confuse me alot..
Reply With Quote Quick reply to this message
  #6  
Old 06-13-2011
bebix's Avatar
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 1,357
Threads: 194
Thanked 3,259 Times in 881 Posts
Reputation: 3269
Smile

Confounding:
Confounding occurs when a factor other than the one you are studying is associated both with the disease and the factor you are studying.

Imagine you are studying the association between an exposure and a disease, for example between drinking coffee and heart disease, and want to decide whether it is a causal association.

Hypothesis = coffee drinking increases the risk of lung cancer

- For example, if drinking coffee is associated with smoking (perhaps people who drink coffee also tend to smoke) the smoking forms a confounding variable because we know that it independently affects heart disease. The result is that there appears to be an association between coffee drinking and heart disease when, in reality, this may be occurring just because the people who drink coffee also smoke, and it is their smoking (not the coffee drinking) which actually causes the heart disease.

Effect modification or interaction: occurs when the effect measure depends on the level of another factor or = when our chosen summary of association differs in different strata.

"The relative risk of ischemic stroke for non-whites compared with whites is about 2 for those aged 35 to 64 years and about 1 for those 65 years of age and above"

Here we have 2 strata (levels):
1.- "young 35-64y/o" = RR of ischemic stroke for non-whites compared with whites is 2
2.- "old >64" y/o" = RR of ischemic stroke for non-whites compared with whites is 1

This is an example of modification of the effect of race by age.
Reply With Quote Quick reply to this message
The above post was thanked by:
dr z (06-13-2011), leo lakhani (06-13-2011), pass7 (06-16-2011), struggle (06-15-2011), tamta (01-03-2015)
  #7  
Old 06-15-2011
USMLE Forums Guru
 
Steps History: Not yet
Posts: 324
Threads: 70
Thanked 236 Times in 143 Posts
Reputation: 246
Default

thanks alott..this is really helpful.
Reply With Quote Quick reply to this message
  #8  
Old 06-15-2011
USMLE Forums Guru
 
Steps History: ---
Posts: 332
Threads: 48
Thanked 168 Times in 107 Posts
Default

Confounding factors are something we strive to avoid when design a study.

Effect modification is something we strive to identify when design a study.
Reply With Quote Quick reply to this message
  #9  
Old 10-26-2014
USMLE Forums Master
 
Steps History: 1+CK+CS
Posts: 1,867
Threads: 149
Thanked 2,085 Times in 1,046 Posts
Reputation: 2105
Default

https://www.pharmacoepi.org/pub/1c22...f-3ef76b968cd0

http://www.nature.com/ebd/journal/v6.../6400356a.html

https://onlinecourses.science.psu.edu/stat507/node/34

http://sphweb.bumc.bu.edu/otlt/MPH-M...unding-EM.html
__________________
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
  #10  
Old 10-26-2014
qirkergaard's Avatar
USMLE Forums Veteran
 
Steps History: Step 1 Only
Posts: 252
Threads: 18
Thanked 129 Times in 98 Posts
Reputation: 139
Default

Also confounding is a type of bias while effect modification is not.
Reply With Quote Quick reply to this message



Reply

Tags
Biostatistics-Epidemiology

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
types of bias ? help kemoo USMLE Step 1 Forum 1 03-29-2011 12:50 PM
This appointment is past the cutoff date for modification. itwasjuly USMLE Step 1 Forum 6 02-12-2011 01:40 PM
Effects of Hyperventilation sam01 USMLE Step 1 Forum 5 04-09-2010 07:19 PM
CCB Effects on the EKG? Yallah USMLE Step 1 Forum 6 04-07-2010 11:47 PM
Selection, Sampling, or Confoundment Bias! DrSeddik USMLE Step 1 Forum 7 12-11-2009 04:50 PM

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)