Title stata.com xi — Interaction expansion Syntax Menu Description Options Remarks and examples Stored results References Also see Syntax

, prefix(string) noomit term(s) xi, prefix(string) noomit: any stata command varlist with terms... where a term has the form i.varname or I.varname i.varname1*i.varname2 I.varname1*I.varname2 i.varname1*varname3 I.varname1*varname3 i.varname1|varname3 I.varname1|varname3 varname, varname1, and varname2 denote numeric or string categorical variables. varname3 denotes a continuous, numeric variable. Menu Data> Create or change data> Other variable-creation commands> Interaction expansion Most commands in Stata now allow factor variables; see [U] 11.4.3 Factor variables. To determine if a command allows factor variables, see the information printed below the options table for the command. If the command allows factor variables, it will say something like “indepvars may contain factor variables”. We recommend that you use factor variables instead of xi if a command allows factor variables. We include [R] xi in our documentation so that readers can consult it when using a Stata command that does not allow factor variables. Description xi expands terms containing categorical variables into indicator (also called dummy) variable sets by creating new variables and, in the second syntax (xi: any stata command), executes the specified command with the expanded terms. The dummy variables created are i.varname creates dummies for categorical variable varname i.varname1*i.varname2 creates dummies for categorical variables varname1 and varname2: all interactions and main effects i.varname1*varname3 creates dummies for categorical variable varname1 and continuous variable varname3: all interactions and main effects i.varname1|varname3 creates dummies for categorical variable varname1 and continuous variable varname3: all interactions and main effect of varname3, but no main effect of varname1 1 2 xi — Interaction expansio