Re: interpretting F & t-vals from regression

Rob Campbell wrote:
I've skimmed the posts and I know a small amount about these issues already
but I'm sure I should learn more: I'm rather new to this game. Your information made me realise that I was
approaching the model building incorrectly rather than misinterpreting
coefficients. For anyone who's interested, here's my take on the situation
now.

You're right that the model was over-specified but I don't think removing
intensity1000 is possible. This is a designed experiment and in the context
of this analysis, that variable is needed to explain what subjects did at
sound durations of 1000 ms.

That is probably a better approach in any case. Though my initial
comments were off target as to exactly what your question was, I think that the over-specification of the model is still the result of improper coding of the factors. You have five levels (k) of duration as an ordered factor. It takes k-1 levels to fully represent that factor in the model. All five levels appeared in your model. As I understand it,
this is the original model you wanted:

lme(outcome ~ intensity + duration + intensity *
duration,data=X, random=~duration|subject/duration )

Your ANOVA table would contain entries for:

(Intercept)
intensity
duration
intensity*duration

and your vector of coefficients would contain:

(Intercept)
intensity
duration100
duration200
duration500
duration1000
intensity:duration100
intensity:duration200
intensity:duration500
intensity:duration1000

The reference category for the ordered factor, duration, is 40. All of
the other coefficients for duration would be interpreted relative to that.
.

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