On Thu, 9 Mar 2000, Kasper Hornb�k wrote:
> I have a question concerning repeated measures analysis. I am not sure
> of whether a linear model with a factor that varies as repeated measures
> are taken (e.g., order or session) is identical to a repeated measures
^^^^^
You mention "order" here but you do not include it in your model below.
Did you intend to?
> analyses. I'll detail the question below.
> I have a within-subject study in which subjects used three methods to
> solve six different tasks. The experiment is run in three sessions, each
> consisting of two tasks.
Are the sessions always in the same order, with the same two
tasks in each session?
> Three of the tasks are very different from the other three tasks.
Does a session always contain two dissimilar tasks, or do some
sessions (perhaps only for some Ss?) contain two similar tasks?
> For analysing this experiment, I plan to use a model like Y[ijkl]:= u+
> subject[i]+ task[j]+ session[k]+ method[l]+ e[ijkl],
> possibly adding interactions between task, method and session. Is this
> a repeated measures analysis or equivalent to a repeated measures
> analysis?
You have not mentioned separate error terms for the
several factors of interest. As I understand "repeated measures
analysis" (and experimental designs corresponding thereto), each repeated
measure would have an error mean square (sometimes called a denominator
mean square) that is formally equivalent to the subject-by-measure
interaction. (This would follow from defining "Subjects" to be a random
factor; ordinarily one would not consider "Subjects" a fixed factor.
Presumably Task, Method, and Session are all fixed factors.)
I gather from your description that Task, Method, and Session
are all repeated factors: that is, all Ss get to do all tasks, in all
sessions, using all methods; although the formal design --
Subjects by Tasks by Sessions by Methods
-- appears to be incomplete in ways that you have not explicitly
described. And it is not clear whether the Ss may perhaps be nested
within an Order factor (if the tasks within each session varied among
Ss, e.g.).
> If not, how should I analyse these data using SAS's repeated measures
> option?
I am not familiar with SAS, and cannot address this question.
-- DFB.
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Donald F. Burrill [EMAIL PROTECTED]
348 Hyde Hall, Plymouth State College, [EMAIL PROTECTED]
MSC #29, Plymouth, NH 03264 603-535-2597
184 Nashua Road, Bedford, NH 03110 603-471-7128
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