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RE: st: ANOVA


From   "Aparna Mathur" <AMathur@AEI.org>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: ANOVA
Date   Tue, 21 Aug 2007 11:12:01 -0400

Great, thanks for your help!

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Steichen,
Thomas J.
Sent: Tuesday, August 21, 2007 11:00 AM
To: statalist@hsphsun2.harvard.edu
Subject: RE: st: ANOVA

Partial SS usually do not add up to the total SS... The only 
(non-pathological) exception is when all your independent 
variables are perfectly uncorrelated. Balanced data is not
immune to this.

Sequential SS will add up to the Total SS.

Partial SS treats each independent variable as if it were the
last variable considered. Thus any SS that might also be due
to some other correlated independent variable is not attributed
to the variable in question. In essence, any SS that might be
explained more than one way is not captured in Partial SS.
Thus the total of Partials is usually less than the Total SS.

Tom

-----------------------------------
Thomas J. Steichen
steicht@rjrt.com
-----------------------------------
 
-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Aparna Mathur
Sent: Tuesday, August 21, 2007 10:00 AM
To: statalist@hsphsun2.harvard.edu
Subject: RE: st: ANOVA

Thanks for responding. Here is the result, and my data set is balanced.
All the variables uptil statepci are dummy variables.


.. anova annpremium alcman drugman mentalman mentparity chiro dental
crating gissue statepci unprt smallfrmemp1 pop medicare agedpop,
continuous (statepci unprt smallfrmemp1 pop medicare agedpop)

                           Number of obs =  137     R-squared     =
0.3686
                           Root MSE      = 782.485     Adj R-squared
=0.2962

                  Source |  Partial SS    df       MS           F
Prob >F
------------+----------------------------------------------------
                   Model |  43614642.7    14  3115331.62       5.09
0.0000
                         |
                  alcman |  1344769.68     1  1344769.68       2.20
0.1409
                 drugman |   2536376.6     1   2536376.6       4.14
0.0440
               mentalman |  1869869.15     1  1869869.15       3.05
0.0831
              mentparity |  610999.438     1  610999.438       1.00
0.3198
                   chiro |  4911205.77     1  4911205.77       8.02
0.0054
                  dental |  1663238.75     1  1663238.75       2.72
0.1019
                 crating |  1743577.33     1  1743577.33       2.85
0.0941
                  gissue |  2879808.29     1  2879808.29       4.70
0.0320
                statepci |  19266358.9     1  19266358.9      31.47
0.0000
                   unprt |  2069599.21     1  2069599.21       3.38
0.0684
             smallfrme~1 |  1557806.53     1  1557806.53       2.54
0.1133
                     pop |  1056893.25     1  1056893.25       1.73
0.1914
                medicare |   4340.0111     1   4340.0111       0.01
0.9330
                 agedpop |  211267.685     1  211267.685       0.35
0.5580
                         |
                Residual |  74698451.1   122  612282.386
------------+----------------------------------------------------
                   Total |   118313094   136   869949.22   









-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of David Airey
Sent: Tuesday, August 21, 2007 9:48 AM
To: statalist@hsphsun2.harvard.edu
Subject: re: st: ANOVA

..

You might post those results in text format and describe if your data  
set is balanced.



> Hi,
>
> My problem is that when I do ANOVA, the sum of the partial SS for  
> all the independent variables in the model does not add up to the  
> Model SS. I have both categorical and continuous variables in my  
> model. Could you help me understand why this might happen?
>
>
> Thanks,
> Aparna
>
>

--
David C. Airey, Ph.D.
Research Assistant Professor

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