1. Matched Pairs, Within-Subjects, and Mixed Designs
Chapter 13
Matched Pairs, Within-Subjects, and Mixed Designs
PowerPoint presentation to accompany Research Design Explained 6h edition;
©2007 Mark Mitchell & Janina Jolley

2. Overview The Matched Pairs Design Pure Within-Subjects Designs
Randomized Within-Subjects Designs
Counterbalanced Within-Subjects Designs
Choosing a Design
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

3. The Matched Pairs Design
Procedure*
Considerations in Using the Matched Pairs Design*
Analysis of Data*
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

4. The Matched Pairs Design: Procedure
Form matched pairs
Randomly assign one member of each pair to the treatment condition, the other to the control condition
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

5. Considerations in Using Matched Pairs Designs
Finding an effective matching variable
Power: A big plus
External validity
Advantage: Don’t restrict subject population (can have heterogeneous group)
Disadvantage: Results may not generalize to participants who haven’t done the matching task
Construct validity weakened because matching may tip off participants about hypothesis
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

6. Analysis of Data in the Matched Pairs Design
Not the between subjects t test (observations are not independent)
Dependent t test: Differences between pairs/ standard error of differences
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

7. Within-Subjects (Repeated Measures) Designs
Considerations in using within-subjects designs
Increased power
Order effects harm internal validity*
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

8. Overview of Four Specific Sources of Order Effects
Practice effects
Fatigue effects
Treatment carryover effects
Sensitization
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

9. Dealing with Order Effects
Minimizing each individual threat (practice, fatigue, carryover, sensitization)
Use as few levels as possible to reduce opportunities for practice, fatigue, carryover, and sensitization
Mixing up sequences to try to balance out order effects: Randomizing and counterbalancing
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

10. Randomized Within-Subjects Designs
Procedure*
Analysis of data*
Summary*
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

11. Procedure
As in all within-subject (repeated measures) designs, each subject is observed in at least two conditions
Randomly determine the sequence of treatments for each participant
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

12. Analysis of Data
Dependent t test (two groups) or Within-Subjects ANOVA (more than two groups)
Within-subjects t (Same test as used for matched pairs analysis)
For each participant, get the difference between his/her score in Conditions 1 vs. his/her score in Condition 2.
Calculate average difference
Divide average difference by standard error of the differences
Look up t in t table under appropriate df (number of participants -1) and significance level.
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

13. Randomized Within-Subjects Designs: Summary
Like all within-subjects designs, quite powerful
Randomization helps balance out order effects, but is there a more effective way?
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

14. Counterbalanced Within-Subjects Designs
Procedure*
Advantages of counterbalancing*
Disadvantages of counterbalancing*
Conclusions about counterbalanced within-subjects designs
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

15. Procedure Randomly assign participants to your sequences
Devise a set of sequences such that
Every condition appears in every position the same number of times (T1 should appear first as many times as it appears last) and
Every condition precedes every other condition just as many times as it follows that condition (For every sequence in which T1 comes before T2, there should be a sequence in which as T1 comes after T2)
Example:
Sequence 1: T1 then T2
Sequence 2: T2 then T1
Randomly assign participants to your sequences
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

16. Advantages of counterbalancing
Balance out routine order effects
Learn about effect of the within-subjects variable of order (trials, position)
Learn about the effect of the between-subjects variable of sequence
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

17. Disadvantages of counterbalancing
May require more subjects
Analysis is more sophisticated
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

18. Counterbalanced Within-Subjects Designs: Conclusions
Balances out routine order effects
Provides information not only about the effect of treatment, but also about the effect of order (trials, position) and sequence
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

19. Choosing an Experimental Design
General considerations*
The two-condition case*
The multiple IV case*
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

20. General considerations:
Pure between-subjects designs may
Have more construct validity because it is harder for participants to guess the hypothesis
Have more internal validity because they are not vulnerable to order effects
Be easier to analyze
Within-subject designs have more power
Whether within-subject designs or between-subjects designs have more external validity may depend on whether the variable is “within-subjects” or “between-subjects” in real life
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

21. Choosing Designs: The Two Conditions Case
Pure between subjects designs
Matched pairs design
Randomized within-subjects designs
Counterbalanced designs
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

22. Choosing Designs: When You Have More Than One Independent Variable
Using a within-subjects factorial design
Using a between-subjects factorial design
Using a mixed design
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley

23. Concluding Remarks
You can now intelligently choose among different types of experimental designs.
You can now propose almost any type of experiment
You can now read almost any write-up of a study that used an experiment
PowerPoint presentation to accompany Research Design Explained 6th edition;
©2007 Mark Mitchell & Janina Jolley