JiscMail Logo
Email discussion lists for the UK Education and Research communities

Help for ALLSTAT Archives


ALLSTAT Archives

ALLSTAT Archives


allstat@JISCMAIL.AC.UK


View:

Message:

[

First

|

Previous

|

Next

|

Last

]

By Topic:

[

First

|

Previous

|

Next

|

Last

]

By Author:

[

First

|

Previous

|

Next

|

Last

]

Font:

Proportional Font

LISTSERV Archives

LISTSERV Archives

ALLSTAT Home

ALLSTAT Home

ALLSTAT  2004

ALLSTAT 2004

Options

Subscribe or Unsubscribe

Subscribe or Unsubscribe

Log In

Log In

Get Password

Get Password

Subject:

Re: Strange Odds ratios

From:

"BXC (Bendix Carstensen)" <[log in to unmask]>

Reply-To:

BXC (Bendix Carstensen)

Date:

Fri, 17 Sep 2004 10:49:48 +0200

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (74 lines)

To Ioanna Gioni:

It would be worth while considering the transformation of the concentration by log10:
This would be a different model, and the corresponding odds-ratio would refer to the
effect of a ten-fold increase in the concentration.

A look at the distribution of the concentartions could give a hint to as whether 
a few very hig concentrations carry most of the information in the linear formulation.

Whether the log-transform is relevant is however not only a statistical but also a 
question of clinical interpretability and relevance.

Bendix Carstensen
----------------------
Bendix Carstensen
Senior Statistician
Steno Diabetes Center
Niels Steensens Vej 2
DK-2820 Gentofte
Denmark
tel: +45 44 43 87 38
mob: +45 30 75 87 38
fax: +45 44 43 07 06
[log in to unmask]
www.biostat.ku.dk/~bxc
----------------------

-----Original Message-----
From: A UK-based worldwide e-mail broadcast system mailing list [mailto:[log in to unmask]] On Behalf Of Edmund J. Bini, M.D., M.P.H.
Sent: Friday, September 17, 2004 3:17 AM
To: [log in to unmask]
Subject: Re: Strange Odds ratios


Hi Ioanna,
Given the large range of your assay, it would be better to calculate the OR for a larger change in the concentration. The OR is 1.004 which means that the odds of having CAD increase by 1.004 for each 1 unit change in your assay. Since the range of your assay is very wide, you would be better off calculating a new variable for your assay by dividing the original concentration by 10 or 100 or some other larger number. If you divide the concentration by 100, then the OR of CAD would be for each 100 unit change in concentration. Hope this helps. Ed  

-----Original Message-----
From: A UK-based worldwide e-mail broadcast system mailing list [mailto:[log in to unmask]] On Behalf Of ioanna gioni
Sent: Thursday, September 16, 2004 12:17 PM
To: [log in to unmask]
Subject: Strange Odds ratios

Dear Allstaters,
I am a little bit puzzled about something and I was wondering if someone had

any suggestion related to this...
I have the concentration results of an assay which clinicians would like to 
use in order to discriminate between subjects of CAD (Coronary Arterial 
Disease) and subjects of no CAD.
The CAD group has 109 subjects and the no-CAD 53.
I try to perform logistic regression modelling for the probability of a 
subject having CAD. However, the results are a little bit confusing. 
Although, the model fits the data well and the p-value of the estimate of 
the assay was highly significant (<0.001), the odds ratio of it came out to 
be 1.004(1.002, 1.006)!!!
Therefore, I got confused.
Then, I implemented a ROC plot which gave me really nice plot of AUC of 
0.895 (the two groups were found to have significantly different means with 
the CAD group having bigger mean   concentration than the no-CAD).
Then I thought that maybe it was the different group sizes (53 non-CAD 
versus 109 CAD). I generated some data so that the group's size would be 
quite similar (106 non-Cad versus 109 CAD this time.) Again, the estimate of

the assay was found to be significant (P<0.001) but the odds ratio 
1.004(1.003, 1.005).
I am thinking that these strange results could be due to the very high range

of concentrations I have to deal with, (47g/ml-10307.40g/ml). Anybody has any suggestion..? Ioanna

_________________________________________________________________
It's fast, it's easy and it's free. Get MSN Messenger today! 
http://www.msn.co.uk/messenger

Top of Message | Previous Page | Permalink

JiscMail Tools


RSS Feeds and Sharing


Advanced Options


Archives

July 2019
June 2019
May 2019
April 2019
March 2019
February 2019
January 2019
December 2018
November 2018
October 2018
September 2018
August 2018
July 2018
June 2018
May 2018
April 2018
March 2018
February 2018
January 2018
December 2017
November 2017
October 2017
September 2017
August 2017
July 2017
June 2017
May 2017
April 2017
March 2017
February 2017
January 2017
December 2016
November 2016
October 2016
September 2016
August 2016
July 2016
June 2016
May 2016
April 2016
March 2016
February 2016
January 2016
December 2015
November 2015
October 2015
September 2015
August 2015
July 2015
June 2015
May 2015
April 2015
March 2015
February 2015
January 2015
December 2014
November 2014
October 2014
September 2014
August 2014
July 2014
June 2014
May 2014
April 2014
March 2014
February 2014
January 2014
December 2013
November 2013
October 2013
September 2013
August 2013
July 2013
June 2013
May 2013
April 2013
March 2013
February 2013
January 2013
December 2012
November 2012
October 2012
September 2012
August 2012
July 2012
June 2012
May 2012
April 2012
March 2012
February 2012
January 2012
December 2011
November 2011
October 2011
September 2011
August 2011
July 2011
June 2011
May 2011
April 2011
March 2011
February 2011
January 2011
December 2010
November 2010
October 2010
September 2010
August 2010
July 2010
June 2010
May 2010
April 2010
March 2010
February 2010
January 2010
December 2009
November 2009
October 2009
September 2009
August 2009
July 2009
June 2009
May 2009
April 2009
March 2009
February 2009
January 2009
December 2008
November 2008
October 2008
September 2008
August 2008
July 2008
June 2008
May 2008
April 2008
March 2008
February 2008
January 2008
December 2007
November 2007
October 2007
September 2007
August 2007
July 2007
June 2007
May 2007
April 2007
March 2007
February 2007
January 2007
2006
2005
2004
2003
2002
2001
2000
1999
1998


JiscMail is a Jisc service.

View our service policies at https://www.jiscmail.ac.uk/policyandsecurity/ and Jisc's privacy policy at https://www.jisc.ac.uk/website/privacy-notice

Secured by F-Secure Anti-Virus CataList Email List Search Powered by the LISTSERV Email List Manager