Module 11: Mixed Design

Single-Subject Design:

Key Idea:

• Measure behavior before and after treatment

• See if treatment causes change

Types of single-subject design:

• A-B → Baseline → Treatment

• A-B-A → Add removal of treatment

• A-B-A-B → Reapply treatment (strongest evidence)

Important:

• If nothing is manipulated → Case study

• If something is manipulated → Experiment

Example Logic:

• Take baseline blood pressure

• Give medication

• Measure again

• Remove medication → measure again

• Reapply → measure again ✅ (best design)

Mixed Design (MOST IMPORTANT):

👉 Combines:

• Between-subjects variable (different groups)

• Within-subjects variable (same people experience all conditions)

🧠 Key Terms:

• Variable (IV) = what you manipulate

• Levels/Conditions = versions of that variable

Example:

IV1 (Between): Caffeine

• No caffeine

• 2 cups coffee

IV2 (Within): Music

• No music

• Music

👉 Each participant:

• Gets ONE caffeine condition

• Experiences BOTH music conditions

🧪 Why mixed design?

• Some variables (like caffeine) can’t easily be repeated

• Others (like music) can be repeated

🔹 4. How to Identify Designs

Situation	Type
One IV, one condition per person	Simple experiment
Multiple IVs, all between	Factorial
Multiple IVs, all within	Repeated measures
Mix of both	✅ Mixed design

🔹 5. Benefits vs Drawbacks:

✅ Pros:

• Combines strengths of both designs

• Fewer participants needed (for within part)

• Can test:

  • Main effects

  • Interaction effects

❌ Cons:

• Order effects (within-subject issue)

• More participants needed (between-subject issue)

• Possible confounds

🔹 6. Control Groups (Know These!)

Type	Meaning
Placebo	Fake treatment
Empty	No treatment
Waiting-list	Treatment later
Treatment-as-usual	Standard treatment

🔹 7. Key Design Considerations:

Ask yourself:

• Which variable is:

  • Within-subjects?

  • Between-subjects?

• What are the conditions/levels?

• When/how is the DV measured?

👥 Participants:

• May need specific criteria (example):

  • No allergies

  • Experience with dogs

  • Similar living conditions

🔬 Validity Tips:

• Randomly assign (for between-subjects)

• Counterbalance order (for within-subjects)

• Remove confounds

🔹 8. Bias Reduction

Blinding:

• Double-blind → neither researcher nor participant knows

• Single-blind → participant doesn’t know

Analysis (Very Important):

What you analyze:

• Manipulation check → did IV actually work?

• Reliability → consistency of measures

• Descriptive stats → averages, demographics

• Inferential stats → differences between groups

Main Test:

👉 ANOVA

• Works with:

  • Multiple IVs

  • Mixed designs

• Tells you:

  • Main effects

  • Interactions

After ANOVA:

👉 Use Post-hoc tests

• To find which groups differ

🔹 10. Example Study (Simplified)

Question:

Does:

• Sleeping with a pet 🐶

• Mindfulness 🧘

👉 Reduce stress?

Results:

• Pet co-sleeping → reduces stress ✅

• Breathing mindfulness → best method ✅

• No interaction effect ❌

🔹 11. Key Takeaways (MEMORIZE):

• Mixed design = within + between

• Within = same people, multiple conditions

• Between = different groups

• Use ANOVA to analyze

• Can test main effects + interactions

🔹 12. Quick Memory Trick:

👉 Mixed = “Some same, some different”

• Same people → within

• Different groups → between