topic create a survival curve not using Lifetest but Phreg in Statistical Procedures

create a survival curve not using Lifetest but Phreg

xianweiw — Sun, 30 Oct 2011 15:20:52 GMT

Hi, I have some questions about how to create survival curve when I consider some other covariates. Although I have referred to Example 64.1 (9.2 user guide), I also face some difficulty. In the example, there are only two interested covariates which are used to divide the two groups and are the category variables. If I have more than two covariates which include even up to 10 covariates or numerical variables, it is not easy to divide groups using the covariates. How should I create the survival curves when I consider much more covariates which include numerical variables? thanks.

create a survival curve not using Lifetest but Phreg

Doc_Duke — Sun, 30 Oct 2011 19:04:17 GMT

Cynthia's response #2 in http://communities.sas.com/thread/31692?tstart=0 is the way to do it unless you are going to stratify on the variables rather than model them. However, you can't stratify on a continuous variable, so you are back to fixing the level of each covariate and computing the estimate of the curve at that level. See Harrell's Regression Modeling Strategies book for more on the theory and process.

I would typically draw a curve for each of the levels of the categorical variable of interest (e.g. treatment) and set the other variables to a default value (e.g. male sex) or to a mean (e.g. for age). You can do this incorporating both stratification and modeling variables.

Doc Muhlbaier

Duke

create a survival curve not using Lifetest but Phreg

xianweiw — Mon, 31 Oct 2011 02:09:46 GMT

Thanks a lot. You are right. Just as what you said, I want to use only one categorical variable of interest (eg. treatment) for stratification while others (confounding factors such as age, sex, hypertension, and so on.) for modeling variables (eg. model death=age sex hypertension; treatment used as stratification). I perform it using SPSS, but can't operate it using SAS. Could you give me suggestion about which books I would refer to? or please provide me with brief codes as an example for me? thanks again.

create a survival curve not using Lifetest but Phreg

Doc_Duke — Mon, 31 Oct 2011 13:23:49 GMT

SAS has Books By Users by both Cantor and Allison on Survival analysis; both are readable. Closer at hand for you is the SAS manual. For instance, example 66.3 in the SAS 9.3 section of the SAS/Stat manual seems to fit your situation pretty well:

http://support.sas.com/documentation/cdl/en/statug/63962/HTML/default/viewer.htm#statug_phreg_sect048.htm

SAS 9.3 has made significant enhancements to the ODS statistical graphics, which may help you on drawing the plots (I don't think that the syntax has changed materially.)

create a survival curve not using Lifetest but Phreg

xianweiw — Tue, 01 Nov 2011 01:05:50 GMT

First, thanks for your help. but example 66.3 in the SAS 9.3 section of the SAS/Stat manual is just generally Cox regression, and doesn't provide how to create survival curve based on groups. I just want to create two survival curve by groups (based on one category variable such as treatment) considering confounding factors like age, sex. I know the Proc Lifetest can create two survival curve without considering other confounding factors.

create a survival curve not using Lifetest but Phreg

Doc_Duke — Tue, 01 Nov 2011 01:47:09 GMT

In SAS 9.3, simply specify /plots=survival. It's in the manual.

create a survival curve not using Lifetest but Phreg

xianweiw — Tue, 01 Nov 2011 06:01:32 GMT

thank you a lot. I will try it according to what you said.