[R-sig-ME] a question about partitioning effects

[John Kingston]

I have a data set in which a group of listeners were asked to categorize 
a series of sounds that stepped incrementally from an [s] to a [sh], as 
in "see" and "she". Members of this series were followed by one of three 
vowels, each one spoken by one of four speakers. Call these the 
"stimulus" characteristics. Past work predicts how differences between 
the vowels and speakers' voices would influence listeners' choice of [s] 
or [sh] as the category to which a particular step in the series 
belongs, and those predictions are clearly confirmed by the results.

In addition to these stimulus characteristics and their predicted 
effects, I also have "listener" characteristics, namely, their gender -- 
there are 23 women and 24 men -- and their scores on Simon Baron-Cohen's 
Autism Spectrum Questionnaire -- it provides a total AQ score and scores 
on five subsets of questions for each listener.

The interest in this study is how a listener's gender and their total AQ 
or subset scores influence the effects of stimulus characteristics on 
their categorization performance. In a mixed effects logistic regression 
model like this, I would ordinarily represent differences between 
listeners as a random effect, but here I also want to include the gender 
and total and subset AQ scores as fixed effects, in interactions with 
the fixed effects that represent the stimulus characteristics.

I should add that I have an analogous data set collected from a 
different group of listeners, evenly divided between women and men, in 
which the stimulus characteristics are the same but the other listener 
characteristics are scores from the five subsets of the Big Five 
personality questionnaire. As the subsets measure what are supposed to 
be independent personality traits, there is no total Big Five score. So 
my question is more general; namely, how do I model the effects of these 
measures of listeners' personality traits while also capturing 
uncontrolled differences between listeners?

-- 
John Kingston
Professor
Linguistics Department
University of Massachusetts
Integrative Learning Center N434
650 N. Pleasant St.
Amherst, MA 01003
1-413-545-6833, fax -2792
jkingston using linguist.umass.edu
http://blogs.umass.edu/jkingstn/