Testing Homoscedasticity

Ujjawal — Fri, 14 Aug 2015 14:45:53 GMT

I am testing heteroscedasticity for Linear Regression Model. I have a categorical independent variable i.e. mealcat having three categories -

1,2 and 3. I am using this equation - api00 = a1 + b1*yr_rnd + b2*mealcat + b3*some_col.

Should i create dummy variables (k-1 categories) for a categorical variable and then change the equation? Is there any CLASS statement to classify categorical variable in PROC MODEL?

api00 = a1 + b1*yr_rnd + b2*mealcat1 + b3*mealcat12 + b4*some_col

Is the above equation correct?

Detailed Code -

proc model data= bhalla.GLMSELECT;

parms a1 b1 b2 b3;

api00 = a1 + b1*yr_rnd + b2*mealcat + b3*some_col;

fit api00 / white pagan=(1 yr_rnd mealcat some_col)

out=resid1 outresid;

run;

quit;

topic Testing Homoscedasticity in Statistical Procedures

Testing Homoscedasticity