Patrick and Greg open with a disagreement about time travel movies, which then somehow devolves into a discussion of alternative approaches to modeling longitudinal data. They agree that a core issue to consider is the separation of within-person and between-person components of change over time, both theoretically and analytically. Throughout the discussion they also mention antici-, hot tub time machine, chipmunks, garbage disposals, digging up John Stuart Mill, whiteboard problems, cats and laser pointers, Roz from Monsters Inc. (she's back!), 3-D dinosaur posters, licking a hot burner, 30th place ribbons, and -pation.