[Air-L] Measuring Interactivity

Hello-- I am a PhD student at Old Dominion University in Virginia, and I am getting ready to start working on my dissertation. I am planning on studying interactivity in online worlds--specifically Second Life. I was wondering if anyone that is doing research that looks at interactivity has found a method for measuring how interactive an experience in an online world is or is not interactive, or if you know of other sources/studies that have measured levels interactivity that would be useful as well. Thanks for your help-- Katie Retzinger