Track C – Chapter 13: Factorial Designs (Two-Way ANOVA)

Scenario: Study Strategy x Test Environment

In this lab, you will work with data from a 2x2 between-subjects factorial design.

  • Factor A: Study Strategy

    • Flashcards

    • Concept Mapping

  • Factor B: Test Environment

    • Quiet room

    • Distracting (background chatter + music)

  • Dependent Variable: Test score (0–100) on a standardized memory test.

The population is set up so that:

  • Students using Concept Mapping score higher overall than those using Flashcards.

  • Students tested in a Quiet room score higher overall than those in a Distracting environment.

  • There is an interaction: Concept Mapping benefits more from a Quiet environment than Flashcards do.

Learning goals

By the end of this lab, you should be able to:

  • Explain what a main effect and an interaction mean in a 2x2 design.

  • Draw and interpret interaction plots.

  • Run a basic two-way ANOVA in Python.

  • Connect the ANOVA table back to the design (Which effect is which?).

Generating the data with PyStatsV1

If you have PyStatsV1 installed from PyPI, you can generate the Chapter 13 data without cloning the GitHub repository.

In a terminal:

python -m venv pystatsv1-env
# On Windows (Git Bash):
source pystatsv1-env/Scripts/activate
# On macOS/Linux:
# source pystatsv1-env/bin/activate

pip install pystatsv1

Now run the Chapter 13 simulator:

python -m scripts.psych_ch13_factorial_anova \
    --n-per-cell 30 \
    --seed 123 \
    --outdir data/psych_ch13

(If you installed PyStatsV1 globally rather than working from the GitHub clone, make sure you run the script from a folder where the Python interpreter can find the scripts module in your environment.)

This will create two CSV files:

  • data/psych_ch13/psych_ch13_factorial_data.csv – one row per participant

  • data/psych_ch13/psych_ch13_factorial_summary.csv – cell means and standard deviations

Suggested analysis steps

  1. Load the data into a pandas DataFrame.

  2. Inspect cell means using groupby (this should match the summary CSV).

  3. Plot the interaction:

    • X-axis: Study Strategy (Flashcards vs Concept Mapping)

    • Lines: Environment (Quiet vs Distracting)

    • Y-axis: Mean test score

  4. Fit a two-way ANOVA model using your preferred library (for example, statsmodels) and identify:

    • Main effect of Study Strategy

    • Main effect of Environment

    • Study Strategy × Environment interaction

  5. Write a short APA-style result paragraph that describes the pattern of means, the ANOVA results, and the interaction.

Connection to Chapter 13 concepts

  • The main effects tell you whether one factor matters on average, collapsing across the other factor.

  • The interaction tests the “it depends” question: Does the effect of Study Strategy depend on the Test Environment?

This lab is designed to reinforce:

  • 13.2 Notation and design structure (2x2 factorial designs)

  • 13.3 Main Effects

  • 13.4 Interactions (spreading vs crossover)

  • 13.5 Simple Main Effects (follow-up questions you might ask after finding an interaction)