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st: creating interaction variables

From   TEWODAJ MOGUES <[email protected]>
To   Stata _ <[email protected]>
Subject   st: creating interaction variables
Date   Mon, 14 Jun 2004 10:52:31 -0400

Richard and Joseph,

Many thanks for your suggestions which I just read upon returning from my short leave. I downloaded xi3, and indeed it seems to be able to do what xi can't, namely interact two continuous variables (which is what I'm interested in). The only downside -- unless I'm missing something about the proper use of xi3 -- is that it automatically includes the lower order terms. Richard, you're right, in many contexts that is good, but oftentimes I just want to do, say, 

tobit y  x1_x2  x3  x4 , ll

However, when I type the command

xi3: tobit y  x1*x2  x3  x4 , ll

I get identical results as if I typed

tobit y  x1  x2  x1_x2  x3  x4 , ll

where I created the interaction x1_x2 through the gen command. So if I don't want lower-order terms, does that mean that I have to resort to generating interactions manually after all? 

Tewodaj Mogues
Dept. of Agricultural and Applied Economics
University of Wisconsin - Madison
427 Lorch St. #317, Taylor Hall
Madison, WI 53706

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