Base levels

    You can specify the base level of a factor variable by using the ib. operator.  The syntax is

           Base         
           operator(*)    Description
           -----------------------------------------------------------------------------------------------------------
           ib#.           use # as base, #=value of variable
           ib(##).        use the #th ordered value as base (**)
           ib(first).     use smallest value as base (the default)
           ib(last).      use largest value as base
           ib(freq).      use most frequent value as base
           ibn.           no base level
           -----------------------------------------------------------------------------------------------------------
            (*) The i may be omitted.  For instance, you may type ib2.group or b2.group.
           (**) For example, ib(#2). means to use the second value as the base.

    Thus, if you want to use group=3 as the base in a regression, you can type

        . regress y  i.sex ib3.group

    You can also permanently set the base levels of categorical variables by using the fvset command.

夏目贵志 发表于 2015-12-14 05:53
可以参考help fvvarlist
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