Design question about repeated measures as nested vs crossed structures
Sorry for the off-topic post, I've been struggling to understand something and don't know where else to turn. I don't understand the distinction between nested and cross classified, and I'd really appreciate if someone can take a moment to set me straight. The example below illustrates my confusion. I often read/hear multivariate measures data described as nested, but this doesn't make sense to me. Here is a typical explanation from http://www.cmm.bris.ac.uk/lemma/mod/lesson/view.php?id=255: "Sometimes we may wish to model more than one response. For example, we may wish to consider jointly English and mathematics exam scores for students because the two responses are likely to be related. We can regard this as a multilevel structure with subjects (English and maths) nested within students as shown in Figure 4.5. ..." (the figure is here: http://www.cmm.bris.ac.uk/lemma/file.php/13/images-C4/image007.gif). To my mind this sounds cross-classified, because each observation is a particular combination of person and exam subject. It seems to make just as much sense to describe these data as participant nested within exam subject, as I've diagrammed here: http://ista.scp.rochester.edu/snapshot1.png. Please, if anyone can clear this up for me I'd really appreciate it. -Ista
Ista Zahn Graduate student University of Rochester Department of Clinical and Social Psychology http://yourpsyche.org