-------------------------------------------------------------------------------
help for avplot3
-------------------------------------------------------------------------------

Partial regression plots for subsamples  

        avplot3 varname ,separate(varname) [ graph_options ]

Description

avplot3 generates "partial regression plots" from an analysis of covariance
model, where a category variable has been included in dummy-variable form among
the regressors along with a constant term (that is, a dummy for all but one
categories appears) and the full set of dummies have been interacted with a
continuous variable. The "partial predictions" of such a model are then
defined, for each category, as the category-specific constant term plus the
category-specific slope multiplied by the continuous variable. Any number of
additional covariates, continuous or discrete, may appear in the regression
model, but do not affect the partial predictions.


Remarks 

One variable must be specified: the continuous variable which has been fully
interacted in the regression model. If there are G categories of the discrete
variable, the continuous variable must be included as G interaction terms, each
named categoryvarname x varname.  See the example below.

The separate option must specify the integer variable (categoryvarname) that
defines the G categories. The model must contain (G-1) dummy variables for all
but one category, and a constant term. It is immaterial which category is
excluded.


Options

graph_options are options of graph, twoway. One may use, for instance, the
    saving option to create a .gph file from the displayed graph.

    The defaults include connect(l) for each subset of predicted values.

separate(varname) specifies the integer variable which defines categories.



Examples

    . use auto

    . drop if rep78==.

    . recode rep78 1/2=2

    . tab rep78,gen(repair)

    . rename rep78 repair

    . forv i=1/4 { g repair`i'xmpg = mpg*repair`i' }

    . reg price length foreign repair2-repair4 repair1xmpg repair2xmpg
        repair3xmpg repair4xmpg

    . avplot3 mpg, sep(repair)



Author

    Christopher F Baum, Boston College, USA
    baum@bc.edu
    
    
Acknowledgements 

    Nick Cox and his routines regplot and keyplot were indispensable in constru
> cting
    this program. Development of the routine was inspired by conversations with
>  Rebekah 
    Coley and Jodi Morris.


Also see

On-line:  help for regress, graph, regdiag, regplot (if installed), sparl (if
                   installed)
 Manual:  [U] 21 Programming Stata