[R] Random effects ANOVA?

Chris Bergstresser chris at subtlety.com
Thu Mar 30 22:06:55 CEST 2006

On 3/30/06, Prof Brian Ripley <ripley at stats.ox.ac.uk> wrote:
> I think you want print or summary rather than anova.  anova() is not very
> useful for aov() models even without error strata.

    That's sort of better.  summary(aov(time ~ drink + Error(video),
data = df));

gives me:

Error: video
          Df Sum Sq Mean Sq F value Pr(>F)
Residuals  2    160      80

Error: Within
          Df  Sum Sq Mean Sq F value    Pr(>F)
drink      1 240.000 240.000  44.211 1.313e-08 ***
Residuals 56 304.000   5.429
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

...what I'm really looking for is something akin to the output from
SAS, which is:

Source     DF     Anova SS    Mean Square   F Value    Pr > F
DRINK       1      240.000        240.000     12.00    0.0742
VIDEO       2      160.000         80.000      4.00    0.2000

> I didn't follow how the videos were chosen.  Random effects apply when the
> 'treatments' were chosen from a large population (which might apply if
> each subject watched (on separate occasions) three videos chosen randomly
> from a larger pool), and if the interest is in the variability of the
> response over videos in the pool.  If subjects were observed more than
> once then I suspect you most likely want a random effect for subjects.

   This problem comes directly from the final for my Experimental
Stats class, which is why it feels a little odd.  The videos were
randomly selected from a library.  Subjects watched one of the three
videos, drank one of the two drinks, and completed the tasks.  There
were no repeated measures, so we can't block on subjects.
   The hypothesis test, according to SAS, treats DRINK*VIDEO as an
error term.  Setting aside whether this is the right analysis, how can
I replicate this analysis in R?

-- Chris

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