topic Proc Genmod Syntax question in Statistical Procedures

Proc Genmod Syntax question

lisahoward — Wed, 25 Mar 2015 14:44:12 GMT

I am trying to create the following table below and am struggling on where to start:

Mock Table1: Treatment Difference in the Headache rate during 90 , 180 and 270 days follow-up period between treated Untreated group (using Poisson Regression)

Headache Incidence Rate				Unadjusted			Adjusted
Treated		Not Treated		RR	95% CI	P value	RR	95% CI	P value
N=xxx		N=xxx
n	%	n	%
xx	x.xx	xx	x.xx	xx.xx	xx.xx-xx.xx	.xxxx	xx.xx	xx.xx-xx.xx	.xxxx

* there will be three rows in total one for 90 days one for 180 days and one for 270 days.

N=number of Subjects;

RR=risk ratio (treated vs. untreated); CI=confidence interval for the RR; RR, 95% CI and p value are from the poisson model.

Unadjusted model: Headache rate = Exposure Group;

Adjusted model: Headache rate =Exposure Group + Age+ index year

I know (or think) I have to use Proc Genmod , but I have never used this procedure before and I am unsure of the syntax used to get the RR CI and P values, or the adjusted and unadjusted stats.

The dataset I am using has the all subjects their exposure, age, index year , flag for headache (0/1) and headache diagnosis date. I am not bothered about the cosmetics of the table format tI can figure that bit out, it is the information inside the table that I need help with

Any help would be gratefully received . Many thanks in advance, Lisa.

Re: Proc Genmod Syntax question

Lida — Fri, 27 Mar 2015 14:18:29 GMT

Hi Lisa, how many exposure groups do you have? Is it a categorical
variable? Is Age continuous?

If you data are coded in this way:

Headache	Person	Exposure (Treated (2) Vs untreated (1)	Age	Year
1	1	1	29	2005
0	1	1	40	2001
1	1	2	45	2015

I believe you can do this to populate your table:

*to populate N fields;

proc freq data=datasetname;

tables Headache*Exposure;

run;

*Unadjusted RR;

proc genmod data=datasetname descending;

class Exposure ;

model Headache =Exposure/ offset=Person dist=p link=log type3;

estimate ' 1 Vs 2' Exposure 1 -1;*Unadjusted RR;

run;

proc genmod data=datasetname descending;

class Exposure Year;

model Headache =Exposure Age Year/offset=Person dist=p link=log type3;

estimate ' 1 Vs 2' Exposure 1 -1; *Adjusted RR;

run;

Re: Proc Genmod Syntax question

lisahoward — Fri, 27 Mar 2015 17:44:04 GMT

Hello, thank you so much for your response. There is one exposure group ( flag = 1) and one untreated group (flag =0). Age is a continuous variable but i may have to add some discrete variables into the adjusted model such as various comorbids e.g. Diabetes etc ( all have a 1 or 0 flag). Would I just add these into the class line of the code and the model line of the code for the adjusted part? May I ask what the line of code does (in particular the -1 bit?

estimate ' 1 Vs 2' Exposure 1 -1; *Adjusted RR

I really appreciate all your help and you taking the time to respond.

Many thanks,

Lisa

Re: Proc Genmod Syntax question

Lida — Fri, 27 Mar 2015 18:00:32 GMT

I think if your variables are coded as dummy vars (1/0) than
you do not need to declare them in class statement. SAS will understand it.
Only Year than should be kept in class statement. In the case of dummy
variables I am not sure if this statement below will work (try it). This
statement allows to estimate a contrast (RR) : group 1 versus 2.

estimate' 1 Vs 2' Exposure 1 -1;

Re: Proc Genmod Syntax question

lisahoward — Fri, 24 Apr 2015 07:03:14 GMT

Apologises for the time delay with regards to my response but I have a quick question regarding the offset statement which =Person. What is the variable 'Person representing' Is this variable holding the total number of patients who had an outcome for that particular exposure? Many thanks.