"Personally, I think the one active ingredient - if there is just one - in OPD that makes it better than other forms is the collaboration that takes place with people from other cultures and backgrounds. There's something about having people from widely different viewpoints in the same learning experience that adds significant value. How might we isolate that one variable? I'm still not exactly sure. As for comparing OPD with traditional PD, that's what I have always hoped to do (see the second image/table above). Still, the more I think about this, the more I'm in agreement that I need to narrow focus even further. Thanks for your input, Chris." - Darren Draper