Popp, D., Laursen, B., Burk, W. J., Kerr, M., & Stattin, H. (2008). Modeling homophily over time with an Actor-Partner Interdependence Model. Developmental Psychology, 44, 1028-1039.
The notes from my Methods class on unit of analysis may be helpful for this topic.
An important issue is whether the two partners in a dyad are distinguishable (i.e., non-exchangeable), as opposed to being indistinguishable (exchangeable). See David Kenny's webpage on dyadic analysis (particularly Topic 3) and the slides from a talk he gave. As Kenny, Kashy, and Cook (2006) state in their book Dyadic Data Analysis:
When dyad members are distinguishable, we estimate the path model or CFA model for each of the two members combined in a single model... However, when members are indistinguishable, it is less clear exactly how to do the analysis. The use of SEM with indistinguishable or exchangeable dyad members has generally been viewed pessimistically... (p. 111).
A suggested reference in this regard is:
Olsen, J. A., & Kenny, D. A. (2006). Structural equation modeling with interchangeable dyads. Psychological Methods, 11, 127-141.
In honor of David Kenny's contribution to dyadic analysis, I've written a song.
As another example of an APIM-type model, see Hye-Sun Ro's dissertation in the online collection to the right.
UPDATE 1 (4/24/12): As we discussed in class, data from both members of a couple (or from a repeated-measures/panel design of individual participants) can be organized two ways. I have created the following graphic to illustrate (you may click on it to enlarge). The "elbow" arrows are meant to convey that, in moving from the "long" to the "wide" format, the second line of couple data (in this case, the wife's) is raised to join the husband's data on the first line. In the longitudinal/panel example, each participant's Time 2 and Time 3 data are moved up to the first line, to join the Time 1 data.
Here's a YouTube video I discovered on SPSS's restructuring technique, which can be used to convert between the above two formats.
UPDATE 2 (4/28/16): A potentially confusing situation can arise when one wants to compare the paths of men and women. Scenarios can exist for using multiple-group modeling or dyadic/APIM analysis. As I wrote on the board (shown below), multiple-group modeling is done when the groups (such as men and women) are independent of each other. Dyadic analysis, on the other hand, is done when there is a connection or interdependence between paired individuals, such as a man and woman in a heterosexual marriage (thanks to OR for taking the picture).
