Re: st: Testing for association

["Roger B. Newson" <r.newson@imperial.ac.uk>]

You really need to define what you mean by "individual association of 
each genotype with the response variable". Specifically, you have to 
specify what you are comparing each genotype with.

You can always define a binary variable for each genotype, and measure 
the association of each of these binary variables with the disease 
outcome. This method compares disease risks (or disease odds) between 
each genotype and all the rest. The main problem with this method is 
that it immediately trebles the number of multiple P-values, compared to 
the number that you would have if you just did a chi-squared for 
association of all genotypes with the disease outcome. This raises 
issues of multiple comparisons.

Alternatively, you might compare disease risks (or odds) between pairs 
of genotypes, using the -punafcc- package for case-control data, or the 
-punaf- package for cohort or cross-sectional data, to estimate risk 
ratios between 2 fantasy scenarios, such as a fantasy scenario in which 
all subjects are AA and a fantasy scenario in which all subjects are CC. 
This method may also raise multiple-comparisons issues. However, if you 
want to use it, then the -punaf- and -punafcc- packages are downloadable 
from SSC.

The packages -qqvalue- and -smileplot- are also downloadable from SSC, 
and can be used to calculate q-values and discovery sets allowing for 
multiple comparisons.

I hope this helps.

Best wishes

Roger


Roger B Newson BSc MSc DPhil
Lecturer in Medical Statistics
Respiratory Epidemiology and Public Health Group
National Heart and Lung Institute
Imperial College London
Royal Brompton Campus
Room 33, Emmanuel Kaye Building
1B Manresa Road
London SW3 6LR
UNITED KINGDOM
Tel: +44 (0)20 7352 8121 ext 3381
Fax: +44 (0)20 7351 8322
Email: r.newson@imperial.ac.uk
Web page: http://www.imperial.ac.uk/nhli/r.newson/
Departmental Web page:
http://www1.imperial.ac.uk/medicine/about/divisions/nhli/respiration/popgenetics/reph/

Opinions expressed are those of the author, not of the institution.

On 26/03/2012 14:20, Shittu, Aminu wrote:
> Hi List members,
> I have a genotype variable with 3 levels (AA, AC and CC); is there a way of testing for individual association of each genotype with the response variable ulcer status (positive and negative) of a patient? They are recorded in 2 separate columns though. I used "tab ulcerstatus genotype, col chi" and got the overall chi2 and p-value.
> Aminu.
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