Track C — Chapter 17 Problem Set (Mixed-Model Designs)

This problem set practices the core ideas of mixed designs:

  • Between-subjects factor: group (Control vs Treatment)

  • Within-subjects factor: time (T1, T2, T3)

  • DV: score

You will interpret:

  1. Main effect of time

  2. Main effect of group

  3. Interaction (group × time)

Run the worked solutions

make psych-ch17-problems

Run only the tests

make test-psych-ch17-problems

Files and outputs

The solution script writes:

  • Synthetic datasets: data/synthetic/

  • Summaries + plots: outputs/track_c/

Exercises

Exercise 1 — Strong interaction

Control stays flat across time; Treatment improves over time.

Questions:

  • Which term (time / group / interaction) is most important here?

  • What would you write in an APA-style sentence?

Exercise 2 — Time only

Both groups improve similarly over time.

Questions:

  • Is there a main effect of time?

  • Is there a group effect?

  • Is the interaction meaningful?

Exercise 3 — Group only (parallel lines)

Treatment is higher overall; the difference is stable across time.

Questions:

  • Is group significant?

  • Why is a non-significant interaction important here?