# st: Two-way anova vs linear regression: how can I understand Partial SS

 From "Airey, David C" <[email protected]> To Statalist <[email protected]> Subject st: Two-way anova vs linear regression: how can I understand Partial SS Date Tue, 5 Jan 2010 20:59:38 -0600

```.

/*
Maybe this doesn't promote understanding, but
can't you calculate it from the bits and pieces left in
-ereturn list- and -return list-? Since,

mss = F * (rss/rdf) * mdf

*/

sysuse auto, clear
anova mpg foreign rep78 foreign#rep78

regress mpg i.foreign##i.rep78
// ereturn list

testparm i.foreign#i.rep78
// return list

display "Interaction partial SS= " r(F)*`rss'/r(df_r)*r(df)

> Dear Statalist,
>
> My question is more about statistics than about Stata, but also so elementary
> that I'd like to post this problem here.
>
> In ANOVA I have difficulty in understanding the notion of Partial Sum of
> Squares - being the default option in Stata's anova.
>
> In understanding statistical methods, I use linear regression (OLS) as a
> reference method, since regression allows me to draw pictures in my mind
> and is a method that I feel comfortable with. ANOVA is not so intuitive
> to me. But since the underlying methods of OLS and ANOVA are essentially
> the same (both General Linear Models - GLMs), I regard the difference
> between these methods as "different interfaces" to the same GLM.
>
> My question is:
> 'How can I obtain the Partial Sum of Squares of each of
> the variables in the case of a two way anova with interaction by us of
> regression analysis?'
>
> or - more applied - :
> How do I get the Partial SS of foreign in:
> *---------------- begin example --------------------------
> sysuse auto, clear
> anova mpg foreign rep78 foreign#rep78
> *------------------ end example -----------------------------
> using regression analysis?
>
> Kind regards,
> GGZ inGeest, Amsterdam.
>
>

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```