Topics Covered
Interaction Terms
Add A:B or A*B to your model and learn what a significant interaction really means.
Simple Slopes
Probe interactions by testing the effect of A at different levels of B.
Plotting Interactions
Visualize interaction effects with ggplot2 — separate lines, colors, and facets.
Key Concepts
- Main effects vs. interaction effects — hierarchy and interpretation
- Centering predictors before creating interaction terms
- Continuous × categorical and continuous × continuous interactions
- When "it depends" is the most honest answer in neuroscience
Homework
- Fit a model with an interaction between drug condition and baseline score
- Probe the interaction using simple slopes analysis
- Create an interaction plot showing separate regression lines per group