Categorical Variables Stata 9

[Alicia Woods]

Hi. I have Stata 9, and I'm trying to run a simple regression with both continuous and categorical variables. When I use the i.variable for my categorical variable, I get an error "operator invalid"

regress herbgrass i.aspect_cat i.cwd_class slope elevation block_id
i: operator invalid

My variables have 3 classes and are numerically coded (1,2,3).
Is the "i." command not available in Stata9? Any suggestions for getting Stata9 to recognize a categorical variable in a linear regression?

Thanks in advance.
Alicia

[Richard Williams]

Look up xi:. Do something like

xi: regress herbgrass i.aspect_cat i.cwd_class slope elevation block_id

You might also just compute the dummies yourself, via something like

tab aspect_cat, gen(aspectc)

I hate xi:, but it may be your easiest option with such an old version of Stata.

[Alicia Woods]

Thanks so much Richard!