R help - Mar 2012 - ANOVA testing over nested MS term

I'm still relatively new to R but was wondering if anyone could help me
force
R to compute the f-statistic etc using the  the nested term rather than the
residual. In my particular case we were nesting a treatment effect by a
replicated tank which was not non-significant enough (p>0.25)to be dropped
from the statistical model.

Here's my code:
summary(analysis1<-aov(Area~Treatment/Tank))

Area is the response variable, treatment is the main effect, nested within a
replicated tank. Thanks so much for your help.

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On Mar 18, 2012, at 08:21 , shoreliner11 wrote:
> I'm still relatively new to R but was wondering if anyone could help me
force
> R to compute the f-statistic etc using the  the nested term rather than the
> residual. In my particular case we were nesting a treatment effect by a
> replicated tank which was not non-significant enough (p>0.25)to be
dropped
> from the statistical model.
Ouch!!!!! Don't _ever_ take high p-values as proof of absence of effect. 
> 
> Here's my code:
> summary(analysis1<-aov(Area~Treatment/Tank))
> 
> Area is the response variable, treatment is the main effect, nested within
a
> replicated tank. Thanks so much for your help.
> 
I.e. Tanks are numbered within Treatments, so that Treatment 1, Tank 1 is
distinct from Treatment 2, Tank 1?

Something like aov(Area~Treatment + Error(Treatment:Tank)) should do it.
There's a wart in aov() causing this sort of model to throw a warning that
"Error() model is singular", for reasons that I never quite fathomed.
An explicit

TrTa <- interaction(Treatment,Tank)

and then using Error(TrTa) gets rid of the warning and provides equivalent
output.

> --
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> 
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-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
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Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com