topic Re: Fitting a quadratic model with a dummy variable involved in SAS Programming

Fitting a quadratic model with a dummy variable involved

JUMMY — Fri, 01 Feb 2019 12:59:14 GMT

I need help with fitting a full quadratic model using PROC REG that contains two linear terms (sweetness and moisturecontent), two quadratic terms (sweetness^2 and moisturecontent^2) and the interaction term for the data below.

data brand;
	input preference moisturecontent sweetness @@;
	if sweetness=2 then dummy=1;
    else if sweetness=4 then dummy=0;
  		dummy_moisture=dummy*moisturecontent;
	datalines;
	64 4 2 73 4 4 61 4 2 76 4 4 72 6 2 80 6 4 
	71 6 2 83 6 4 83 8 2 89 8 4 86 8 2 93 8 4
	88 10 2 95 10 4 94 10 2 100 10 4
	;
run;
proc print;
run;

Please use ONLY PROC REG in explaining.

Re: Fitting a quadratic model with a dummy variable involved

PaigeMiller — Fri, 01 Feb 2019 13:13:36 GMT

@JUMMY wrote:

Please use ONLY PROC REG in explaining.

I object to this restriction. You are only making life harder for yourself.

So, for anyone else reading along, this should work:

proc glm data=have;
    class sweetness;
    model preference = sweetness | moisturecontent moisturecontent*moisturecontent;
run;
quit;

Re: Fitting a quadratic model with a dummy variable involved

JUMMY — Fri, 01 Feb 2019 13:18:48 GMT

@PaigeMiller, I need the diagnostic plots. GLM doesn't help in writing out an equation. There are no coefficients to use in deriving or fitting my model. Thats why I opted for PROC REG please.

Re: Fitting a quadratic model with a dummy variable involved

Rick_SAS — Fri, 01 Feb 2019 13:26:53 GMT

Your last line makes me wonder whether this is for a class? If so, you should say so. It enables the experts to give you hints and suggestions that can lead you towards the answer, instead of solving the problem for you.

You can use the GLMMOD procedure to generate the design matrix that contains the dummy variables.

proc glmmod data=brand outdesign=Design;
model preference = moisturecontent sweetness 
                   moisturecontent*moisturecontent
                   moisturecontent*sweetness 
                   sweetness*sweetness;
run;

The columns od the DESIGN data set contain the dummy variables, which you can then use in PROC REG:

proc reg data=Design;
model preference = col2-Col6;
quit;

In spite of your admonition to "ONLY [use] PROC REG in explaining," I feel compelled to point out that it is much easier to use PROC GLM and the CLASS statement:

proc glm data=brand ;
model preference = moisturecontent sweetness 
                   moisturecontent*moisturecontent
                   moisturecontent*sweetness 
                   sweetness*sweetness;
run;

Re: Fitting a quadratic model with a dummy variable involved

JUMMY — Fri, 01 Feb 2019 13:29:48 GMT

@Rick_SAS, I feel honored to have you comment on my post. Thank you so much for taking time to explain this to me.