[R] lme newbie question

[JRG]

On 11 Jun 04, at 20:12, Christoph Lehmann wrote:

> Hi
> I try to implement a simple 2-factorial repeated-measure anova in the
> lme framework and would be grateful for a short feedback
> 
> -my dependent var is a reaction-time (rt), 
> -as dependent var I have 
>    -the age-group (0/1) the subject belongs to (so this is a
>     between-subject factor), and 
>    -two WITHIN experimental conditions, one (angle) having 5, the other
>     3 (hands) factor-levels; means each subjects performs on 3 * 5 = 15
>     different task diffiulties
> 
> Am I right in this lme implementation, when I want to investigate the
> influence of the age.group, and the two conditions on the rt:
> 
> 	my.lme <- lme(rt ~ age.group + angles * hands, data = my.data, random =
> ~ 1 |subject)
> 
> then I think I would have to compare the model above with a more
> elaborated one, including more interactions:
> 
> 	my.lme2 <- lme(rt ~ age.group * angles * hands, data = my.data, random
> = ~ 1 |subject)
> 
> and comparing them by performing a likelhood-ratio test, yes?
> 
> I think, if I would like to generalize the influence of the experimental
> conditions on the rt I should define angles and hands as a random
> effect, yes? 
> 

Perhaps I've missed something here, but wouldn't your ability to generalize about the experimental conditions depend, in part, 
on how their levels were selected?  Were the angles randomly sampled?  Were the hands randomly sampled (not sure what 
that would mean)?  If not, how does defining these conditions to be random effects in a model enable valid generalization?

---JRG



John R. Gleason

Syracuse University
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