topic Re: Categorical time dependent covariate in Cox in SAS Programming

Categorical time dependent covariate in Cox

haoduonge — Sun, 04 Apr 2021 20:03:44 GMT

Hi all,

I found this topic was discussed before. I figured out how to use it for dichotomous or continuous variable, but I don't find any example in which time dependent covariate is categorical (0, 1,2,3).

Please share if you have coding example modeling categorical time dependent variable/covariate.

Thank you!

Hao

https://support.sas.com/documentation/cdl/en/statug/63347/HTML/default/viewer.htm#statug_phreg_sect050.htm

Re: Categorical time dependent covariate in Cox

PhilC — Tue, 06 Apr 2021 13:58:48 GMT

Categorical and ordinal variables should be converted to dichotomous variables. Why. There are more intricate explanations, so long story short: Grade level, e.g. in the US: K, 1 through 12, is an ordinal variable. It can't be used as a analysis variables because there is no sense in taking the difference in grade nor the mean of grade. K, 1 through 12 are categories, they would work equally well if they were labeled A,B..M. being ordinal, there is only the set mathematical relationships that begin grade K is less than grade 1 through 12, 1 less than grade 2, etc.

Look at page 13 of this pdf to see how Gender can be coded with a dichotomous variable scheme. Mind you this is not the only way to do it.

referring to: SD-29.pdf (lexjansen.com)

Re: Categorical time dependent covariate in Cox

haoduonge — Tue, 06 Apr 2021 20:34:45 GMT

Thanks!