topic Re: How to get the P-trend from proc genmod procedure in Statistical Procedures

How to get the P-trend from proc genmod procedure

critiasun — Wed, 11 Nov 2020 12:42:26 GMT

Good evening! Everyone! I am working on Generalized Linear Model，Variable X2 has 4 value(1,2,3,4), now I can see a trend from Variable X2 , but I can not find the default parameter to get the P-trend, How to do it?

Re: How to get the P-trend from proc genmod procedure

StatDave — Wed, 11 Nov 2020 14:43:48 GMT

If you want to test for trend over the levels of X2, that implies that its levels are ordered. If the values 1,2,3,4 reflect the spacing between its levels, then specify X2 in the MODEL statement but not in the CLASS statement. The single p-value that you get for X2 will be a test of its linear effect on the response function.

Re: How to get the P-trend from proc genmod procedure

critiasun — Thu, 12 Nov 2020 00:36:44 GMT

I had gotten rid of X2 from class statement, the results showed as follow:

what you mean is this results(ChiSquare=120.96, P<0.0001) is the linear effect(P-trend) ?

Re: How to get the P-trend from proc genmod procedure

StatDave — Thu, 12 Nov 2020 14:22:35 GMT

No, those are results from CONTRAST or ESTIMATE statements. I am referring to the test of X2 in the Parameter Estimates table.

Re: How to get the P-trend from proc genmod procedure

critiasun — Thu, 12 Nov 2020 16:49:35 GMT

Could you show me how to write the statement， can you give me an example?

Re: How to get the P-trend from proc genmod procedure

StatDave — Thu, 12 Nov 2020 21:03:56 GMT

proc logistic;
model y(event="1") = x2;
run;

The test of X2 is a test of its linear effect on the logit (log odds). You could have additional variables in the model and that is still true.

Re: How to get the P-trend from proc genmod procedure

critiasun — Fri, 13 Nov 2020 00:49:19 GMT

If I use the 'proc genmod' procedure, can it be like this:

proc genmod;
model y("event=1")=X2;
run;

Re: How to get the P-trend from proc genmod procedure

StatDave — Fri, 13 Nov 2020 14:32:13 GMT

If you are fitting a logistic model, the best tool is PROC LOGISTIC. PROC GENMOD can also be used, but since GENMOD fits a broader class of models than just logistic models, you need to specify the DIST=BINOMIAL option to tell GENMOD to fit a logistic model:

model y(event="1") = x2 / dist=binomial;

Note that this assumes that the response variable, Y, takes on values 0 or 1 and that Y=1 is considered the event of interest.

Re: How to get the P-trend from proc genmod procedure

critiasun — Sun, 15 Nov 2020 14:43:56 GMT

I fitted GENMOD model as follow:
proc genmod desc data=tot;
model GDM= X2/ dist = binomial;
run;

the results as follow:

Is this the linear results like trend?

Re: How to get the P-trend from proc genmod procedure

StatDave — Tue, 17 Nov 2020 02:59:24 GMT

Yes. The large Wald chi-square for X2, 355.62, is significant (p<0.0001) indicating a non-zero trend on the log odd of the event level which is the first level of GSM as shown in the Response Profile table.

Re: How to get the P-trend from proc genmod procedure

critiasun — Tue, 17 Nov 2020 11:32:39 GMT

Question has been solved with your help! Thank you very much !