Stata tip 106: With or without reference
Maarten L. BuisThe Stata Journal (2012) Vol. 12 No. 1, pp. 162-164.
Abstract
When including a set of indicator variables (often called dummy variables) the standard approach is to leave one category out, the so-called reference category. It is possible to include an indicator variable for the reference category if one excludes the constant, and this can provide a useful alternative view on the same model. This idea can also be extended to interaction effects. In this tip I discuss a couple of examples of how to use this trick.
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Additional material
- A translation of the example to Stata ≤ 10