topic Re: How to find the the "constant is zero" in SAS system ? in SAS Software for Learning Community

How to find the the "constant is zero" in SAS system ?

Olivia0223 — Fri, 14 Apr 2023 02:04:58 GMT

Hello I 'am new ,I need to help !!How to find the the "constant is zero" in SAS system ?

Re: How to find the the "constant is zero" in SAS system ?

whymath — Fri, 14 Apr 2023 06:19:06 GMT

There is a "noint" option when you are using "model" statement in SAS.

Re: How to find the the "constant is zero" in SAS system ?

Olivia0223 — Fri, 14 Apr 2023 14:31:48 GMT

I can not find that..

Re: How to find the the "constant is zero" in SAS system ?

Olivia0223 — Fri, 14 Apr 2023 14:34:49 GMT

Thank you!! I still can not find that...😭

Re: How to find the the "constant is zero" in SAS system ?

tom_grant — Fri, 14 Apr 2023 14:52:48 GMT

Just Un-check the Intercept on the Edit Model screen

Re: How to find the the "constant is zero" in SAS system ?

PaigeMiller — Fri, 14 Apr 2023 14:57:57 GMT

I point out that there are times when using no intercept/"constant is zero" is a very poor choice. In fact, it is rare when it is the right choice. So unless you have a good reason for using no intercept/"constant is zero", don't do it.

Re: How to find the the "constant is zero" in SAS system ?

Olivia0223 — Fri, 14 Apr 2023 15:25:18 GMT

Thank you very much!!

I got the answer.

Re: How to find the the "constant is zero" in SAS system ?

Olivia0223 — Fri, 14 Apr 2023 15:32:01 GMT

Because my first mode was bad so I want to remove the intercept.

Re: How to find the the "constant is zero" in SAS system ?

Reeza — Fri, 14 Apr 2023 15:45:54 GMT

0.8 is a decent model, 0.98 is a model is likely overfit.

Re: How to find the the "constant is zero" in SAS system ?

PaigeMiller — Fri, 14 Apr 2023 16:32:01 GMT

It has been a long time since I did the math, but I believe that R-squared without an intercept has to be interpreted differently than with an intercept, and so the two R-squared values are not directly comparable.

Adding: here is a discussion, which includes the math, explaining why you shouldn't compare R-squared with intercept to R-squared without intercept. https://stats.stackexchange.com/questions/26176/removal-of-statistically-significant-intercept-term-increases-r2-in-linear-mo

Re: How to find the the "constant is zero" in SAS system ?

Olivia0223 — Fri, 14 Apr 2023 16:39:51 GMT

When I working in the SAS system the answer show looks different,I saw the coefficient intercept p value is 0.78(over 0.05) which suggests that the intercept variable is not statistically significant.

Re: How to find the the "constant is zero" in SAS system ?

PaigeMiller — Fri, 14 Apr 2023 17:35:16 GMT

@Olivia0223 wrote:

When I working in the SAS system the answer show looks different,I saw the coefficient intercept p value is 0.78(over 0.05) which suggests that the intercept variable is not statistically significant.

Intercept not significant is not really a valid reason to remove it from the model. You are forcing the model through the point x=0 y=0 which may not be a good thing to do in most cases — this is not about statistical significance. You cause the other parameter estimates to be biased; and the residuals will not add to zero. https://stats.stackexchange.com/a/7950

Lastly, just do a plot of the fit between the two different regressions. Here's made up data, we add a certain amount of soap to a dish of water, agitate the water, and then measure the height of the suds formed.

data suds;
    input soap suds;
    cards;
0.6 1.1
0.7 1.2
0.8 1.33
0.9 1.39
1 1.47
1.2 1.6
;
title 'Model with Intercept';
proc reg data=suds;
    ods select fitplot;
    model suds=soap;
run; quit;
title 'Model without Intercept';
proc reg data=suds;
    ods select fitplot;
    model suds=soap/noint;
run; quit;

Here are the plots, by looking at them, which do you think fits better?

Re: How to find the the "constant is zero" in SAS system ?

Olivia0223 — Fri, 14 Apr 2023 18:17:14 GMT

thank you for your explaining, let me think about how to fix my model.😂