[R] Why do I get (not estimable) in this aov data

[peter dalgaard]

On Nov 30, 2010, at 13:58 , Hedberg Peter wrote:

>> aov_data
> Call:
>   aov(formula = Species1 ~ Site + Obstacle + Treatment + as.factor(Dist_Obstacle) + 
>    as.factor(Dist_start) + Transect + Mainplot + Obsplot)
> 
> Terms:
>                     Site  Obstacle Treatment as.factor(Dist_Obstacle) as.factor(Dist_start)  Transect   Obsplot Residuals
> Sum of Squares   2143.984   446.274   340.042                  736.073               173.707   800.270  4014.378 17238.625
> Deg. of Freedom         2         1         1                        4                    3        10        60       271
> 
> Residual standard error: 7.97566 
> 27 out of 109 effects not estimable
> Estimated effects may be unbalanced
> 
> 
> 
> My question is why do I get "effects not estimable", and "effects may be unbalanced). I have checked the data and it is balanced.

Unfortunately, your attachment did not contain the data, but the sum of the Deg. of Freedom  above is 352, suggesting that the observation count is 353, which is prime, so I find it difficult to believe that you have balanced data in the sense of a complete factorial design, even for a subset of your factors. A complete factorial with those DF would take more than 160000 observations!

I suspect that aov() is simply the wrong tool for these data. lm() will do it, but watch out for the aliased effects.

-- 
Peter Dalgaard
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com