topic Re: 1) are the two lines coincident? 2) are the slopes different? 3) are the intercepts different? in New SAS User

1) are the two lines coincident? 2) are the slopes different? 3) are the intercepts different?

swBuenoLopez — Tue, 31 Oct 2023 02:55:14 GMT

I want to answer the following questions:

are the lines coincident?
are the slopes different?
are the intercepts different?

For that, I have used the following piece of code:

PROC REG DATA=ALL;

MODEL Y = X Z1 Z2 XZ1 XZ2 Z1Z2;

INTERCEP: TEST Z1, Z2;

SLOPE: TEST XZ1, XZ2;

COINCID: TEST Z1, Z2, XZ1, XZ2;

RUN;

How can I interpret the results?

Comments will be deeply appreciated...

Best,

Santiago

Re: 1) are the two lines coincident? 2) are the slopes different? 3) are the intercepts different?

PaigeMiller — Tue, 31 Oct 2023 09:32:38 GMT

More explanation is needed.

What are the variables X Z1 Z2 XZ1 XZ2 Z1Z2?

Re: 1) are the two lines coincident? 2) are the slopes different? 3) are the intercepts different?

swBuenoLopez — Tue, 31 Oct 2023 15:44:59 GMT

X is a continuous explanatory variable; Y is a continuous dependent variable, Z1 and Z2 are dichotomous variables. An example of the data is:

Y	X	Z1	Z2
0.38448	11134.94	1	0
0.42872	10280.34	1	0
0.45391	12595.40	1	0
0.26954	7461.27	1	0
0.49276	13352.59	1	0
1.09706	33692.40	1	0
0.31529	8987.04	1	0
0.20629	5190.80	1	0
0.49011	15962.34	1	0
0.23585	6454.96	1	0
0.54901	14717.25	1	0
0.26269	7757.72	1	0
0.62173	14394.44	1	0
0.60383	18041.02	1	0
0.47756	13406.98	1	0
0.44168	11272.19	1	0
0.09205	2349.10	1	0
0.32221	8780.78	1	0
0.19188	5586.24	1	0
0.19467	4797.40	1	0
0.08793	2121.80	1	0
0.13247	3744.60	1	0
0.22353	5683.04	1	0
0.09343	2175.01	1	0
0.47902	13764.63	0	1
0.21821	5703.75	0	1
0.08321	1954.22	0	1
0.15906	4490.16	0	1
0.50418	15138.00	0	1
0.08847	2178.00	0	1
0.16686	4471.20	0	1
0.17571	4435.76	0	1
0.27287	7337.30	0	1
0.05631	1362.18	0	1
0.13135	3717.12	0	1
0.41391	11741.91	0	1
0.13025	3207.24	0	1
0.34055	10097.38	0	1
0.32904	8126.60	0	1
0.47509	12354.75	0	1
0.80383	23064.00	0	1
0.66650	18758.08	0	1

Re: 1) are the two lines coincident? 2) are the slopes different? 3) are the intercepts different?

PaigeMiller — Tue, 31 Oct 2023 21:56:21 GMT

I'm surprised you don't get an error from PROC REG since Z1 and Z2 are perfectly correlated. But I really don't use PROC REG much any more.

I would do this in PROC GLM (in which case Z2 is not needed)

proc glm data=have;
    class z1;
    model y=x z1 x*z1;
run; quit;

If the statistical test of the effect of Z1 is statistically significant then the intercepts are different. If the effect of X*Z1 is significant, then the slopes are different. I might want to think about this a little more, but if the tests for both Z1 and X*Z1 are both not significant, then the lines are coincident (except for random noise).

Re: 1) are the two lines coincident? 2) are the slopes different? 3) are the intercepts different?

ballardw — Tue, 31 Oct 2023 16:49:39 GMT

Sometimes a picture is worth a lot of tests:

proc sgplot data=have;
   reg x=x y=y/group=z1;
run;

Or set ods graphics one and use the PLOTS statement of Proc Reg or Proc GLm or ...

Re: 1) are the two lines coincident? 2) are the slopes different? 3) are the intercepts different?

swBuenoLopez — Tue, 31 Oct 2023 18:37:36 GMT

Thanks so much, ladies and gentlemen...your support is deeply appreciated!!!!

Re: 1) are the two lines coincident? 2) are the slopes different? 3) are the intercepts different?

swBuenoLopez — Wed, 01 Nov 2023 17:33:25 GMT

Thanks so much for your support...

Re: 1) are the two lines coincident? 2) are the slopes different? 3) are the intercepts different?

PaigeMiller — Wed, 01 Nov 2023 18:04:19 GMT

So in your original problem statement, you were performing statistical testing in PROC REG. Then you mark correct the answer which just draws plots. I don't think plots is the correct answer, although it may be very helpful to have a plot, there is no statistical testing going on.