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st: RE: adding mean plot to anovaplot


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: adding mean plot to anovaplot
Date   Mon, 1 May 2006 23:36:33 +0100

For those not in the know, -anovaplot- is 
a user-written command. 

. search anovaplot 

points to a write-up: 

SJ-4-4  gr0009  . . . . . . . . . . Speaking Stata: Graphing model diagnostics
        (help anovaplot, indexplot, modeldiag, ofrtplot, ovfplot,
        qfrplot, racplot, rdplot, regplot, rhetplot, rvfplot2,
        rvlrplot, rvpplot2 if installed)
        Q4/04   SJ 4(4):449--475
        plotting diagnostic information calculated from residuals
        and fitted values from regression models with continuous
        responses

Now on the question, I'm not clear what John wants 
that -anovaplot- does not provide, 
as the main purpose of -anovaplot- is precisely to 
show means according to anova factors. 

Thus 

. sysuse auto, clear

. anova mpg rep78 foreign

                           Number of obs =      69     R-squared     =  0.2825
                           Root MSE      = 5.16246     Adj R-squared =  0.2256

                  Source |  Partial SS    df       MS           F     Prob > F
              -----------+----------------------------------------------------
                   Model |  661.189524     5  132.237905       4.96     0.0007
                         |
                   rep78 |  179.189006     4  44.7972516       1.68     0.1655
                 foreign |  111.773747     1  111.773747       4.19     0.0447
                         |
                Residual |  1679.01337    63  26.6510059   
              -----------+----------------------------------------------------
                   Total |   2340.2029    68  34.4147485   

. anovaplot

gives me two parallel segmented lines shows means fitted 
as a function of the factors, plus point symbols for the 
data. 

(For some unknown reason, ANOVA people tend to plot just 
means, and not the original data, but the author of -anovaplot-
evidently does not approve. Any regression person
showing just a straight line would get told pretty promptly
to add the data by any competent refereee or boss.) 

Nick 
n.j.cox@durham.ac.uk 

John Novak
 
> I would like to add a plot of the treatment means collapsed 
> across the by 
> variable to an -anovaplot-.  I have done this:
> 
> #delimit ;
> quietly anova y a b a*b;
> anovaplot ,
>          scatter(msymbol(i) xsize(3) ysize(3) name(by_b, replace))
>          plot(mband y a) ;
> delimit cr
> 
> It is almost what I want, but adds the median band instead of a mean 
> band.  Does anyone know how I can accomplish the same effect, 
> but with 
> means instead of medians?

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