### COBOT: Conditional Ordinal-By-Ordinal Test

URL of this page:

http://biostat.mc.vanderbilt.edu/OrdinalRegression
We developed a method for testing for association between two ordinal variables,

*Y* and

*X*, while adjusting for covariates

*Z*. The data analysis program (

COBOT-analysis.r) is written in R (

www.r-project.org). The main analysis functions are

`COBOT.emp()`

and

`COBOT.scores()`

for calculating empirical and asymptotic p-values when proportional odds models are used to model P(

*Y*|

**Z**) and P(

*X*|

**Z**). Please see the beginning lines of the file for detailed descriptions.

##### Version history

12/06/2010: Old version did not work for ordinal variables with 3 levels. The new version should work.

12/04/2011: The R Design package has been replaced by R rms package. The code is updated to reflect the change.

07/23/2012: a bug fix in the

`ifelse()`

calls inside function

`COBOT.scores()`

.

##### Simulation code and other simulation results

Our simulation code is in

COBOT-simulation.r.

Other simulation results not included in the article:

ordinal-otherresults.pdf
##### Software package

The code given above has now been incorporated into an R package, PResiduals. This package is freely available at

http://cran.r-project.org/web/packages/PResiduals/index.html.

##### Contact and paper

For questions, please contact

cxl791@case.edu or

bryan.shepherd@vanderbilt.edu .

The paper that describes the method is:

Li C, Shepherd BE (2010) Test of association between two ordinal variables while adjusting for covariates.

*Journal of the American Statistical Association* 105:612-620