[R] lme() direction

Mike Lawrence mike at thatmike.com
Sat Feb 7 18:37:06 CET 2009

And if I decided to ignore the "type" variable altogether and simply
use the continuous "valence" variable, this is what I'd use?

	fixed = rt~valence*color
	, data = a
	,random = ~1|id

I also have continuous luminance measurements of each color that vary
from participant to participant (we used different monitors). If I
were interested in luminance *instead* of color, would the following
be appropriate, or do I need to do something special to account for
the fact that each participant has different values of luminance?

	fixed = rt~valence*luminance
	, data = a
	,random = ~1|id

On Sat, Feb 7, 2009 at 12:34 PM, Dieter Menne
<dieter.menne at menne-biomed.de> wrote:
> Mike Lawrence <mike <at> thatmike.com> writes:
>>Would it improve things if "type" were a continuous variable rather
>>than categorical? I chose words at the extreme ends of a valence
>>rating scale but I still have the raw valence ratings for each word.
>> >
>> > With the interaction, the extreme would be
>> > summary(lme(rt~type*color*word, data=a,random=~1|id))
>> >
>> > or, less extreme
>> >
>> > summary(lme(rt~type*color+color:word, data=a,random=~1|id))
> ..
> Something like
> summary(lme(rt~type*color+color:as.numeric(word), data=a,random=~1|id))
> (please replace as.numeric() by the raw valence, the example above it
> simply wrong)
> could gain you a few degrees of freedom if you are willing to accept the
> linear hypothesis. And as there is something like raw valence, one should
> not throw away details about a-priori ordering in favor of a categorical
> hypothesis.
> Dieter
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Mike Lawrence
Graduate Student
Department of Psychology
Dalhousie University

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