Our first meeting will be Thursday, July 19, from 12-1 in 143 Straub. Here’s the agenda:

1. Introductory and organizational stuff. We’ll talk about why we’re all here and what we are hoping to accomplish. We will also talk about possible topics for future meetings.

2. For our first topic, we thought it would be fun to read and discuss a recent article on analyzing stimulus effects in experiments.

Say you’re running an experiment that has multiple trials within each of 2 or more conditions, and each trial presents a stimulus drawn from a larger possible set. If that sounds vague it’s because it is a pretty common situation in cognitive and social-cognitive experiments. (The article has some specific examples from social psych; see if you can think of others from your field.) The classic PSY 611 approach has 2 steps: in step 1 you average together responses from all trials within each condition, and then in step 2 you run an ANOVA on the condition averages. That approach makes the experiment amenable to the assumptions of ANOVA in step 2. But it ignores the variability among stimuli and the fact that you are making generalizations about some larger hypothetical population of stimuli. Judd et al. discuss some statistical problems with the classical approach, and show how to used mixed models (a.k.a. multilevel models) to model stimulus effects and test your hypotheses in the same analysis:

Judd, C. M., Westfall, J., & Kenny, D. A. (2012). Treating stimuli as a random factor in social psychology: A new and comprehensive solution to a pervasive but largely ignored problem. Journal of Personality and Social Psychology, 103, 54-69. [The link should take you to a full text copy if you are on campus or on the VPN.]

To ground the discussion a bit, Karyn is going to talk about an example of how she modeled trial-level effects in a recent paper of hers. If you’re so inclined, you are welcome to read that paper too (but we aren’t expecting you to).

We also encourage you to think of examples from your own research or other work you have read, and come ready to talk about them.

See you on the 19th!