In your first syntax:
xi: logistic <DV> i.snp sex ethnics
The model assumes that "ethnics" is an ordinal value. The coefficient is giving you the change in the dependent variable, DV, for each unit change in ethnics. This doesn't make any sense because "ethnics" is a 4-level categorical variable (nominal), not an ordinal variable. Treat your ethnics variable the same way you treated your SNP variable.
Your second syntax is the correct approach:
xi: logistic <DV> i.snp sex i.ethnics
-p
___________________________________
Paul F. Visintainer, PhD
Epidemiology and Biostatistics Core
Baystate Medical Center
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of [email protected]
Sent: Monday, January 11, 2010 8:03 AM
Subject: st: how to adjust for covariates?
Hello list,
Date: Mon, 11 Jan 2010 13:49:52 +0100
Message-ID: <[email protected]>
From: [email protected]
To: undisclosed-recipients:;
I'm doing a SNP analysis using the xi:logistic function.
To exclude possible confounder, I'm adjusting my calculations for different variables, e.g. sex and ethnics.
My study population consists of 4 different ethnicities, coded as 1 2 3 4. sex is coded 1 2. SNPs are coded 1 2 3 (e.g. CC/CT/TT).
I don't understand the following:
When I calculate:
xi:logistic i.snp sex ethnics
i get different results to
xi:logistic i.snp sex i.ethnics
Why is that, and what is the correct way to adjust for ethnics, using i.ethnics or just ethnics?
Thank you,
Kristina
*
* For searches and help try:
* http://www.stata.com/help.cgi?search
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
----------------------------------------------------------------------
CONFIDENTIALITY NOTICE: This email communication and any attachments may contain confidential and privileged information for the use of the designated recipients named above. If you are not the intended recipient, you are hereby notified that you have received this communication in error and that any review, disclosure, dissemination, distribution or copying of it or its contents is prohibited. If you have received this communication in error, please reply to the sender immediately or by telephone at (413) 794-0000 and destroy all copies of this communication and any attachments. For further information regarding Baystate Health's privacy policy, please visit our Internet web site at http://www.baystatehealth.com.
*
* For searches and help try:
* http://www.stata.com/help.cgi?search
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
