R help - Dec 2012 - Nested ANOVA

Hi all,

I'm trying to perform a nested ANOVA, in which "Rewetted" is the
main
factor and "Position" is a fixed factor nested in
"Location". I'm
interested in the effect of "Rewetting" and "Position" on
the dependent
variable (in this case called N), and also in the interaction between these
factors. I tried finding this using this script:

summary(aov(data=data1, N~Rewetted*Location+Error(Position/Location))

This yielded the following output:

Error: Position
          Df Sum Sq Mean Sq F value Pr(>F)
Residuals  2 0.1625 0.08125

Error: Position:Location
          Df Sum Sq Mean Sq F value Pr(>F)
Rewetted   1  29.65  29.650   5.664 0.0321 *
Location   6  42.61   7.102   1.357 0.2975
Residuals 14  73.29   5.235
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05
'.' 0.1 ' ' 1

Error: Within
          Df Sum Sq Mean Sq F value Pr(>F)
Residuals 48  109.9   2.289

As you can see, there is no P-value for Error: position, so I can't say
what the effect of Position is. According to my supervisor this is because
something in the formulation of the script is wrong, but he won't tell me
what (or he doesn't actually know...). What should I change?

Thanks,
Annette

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