Ch. 9

Adding to your flow chart...

Within-subjects design: where every participant serves in every group/receives all levels of the IV.

• Goal of experimentation/within-subjects design:

reducing subject variability

Advantages of Within-Subjects designs:

• fewer subjects
• reduced error term

Disadvantages

• sensitive to time-related effects
• order effects



• practice effects













• fatigue effects

Possible Solutions

• Complete counterbalancing: when (1) each condition must occur an equal number of times and (2) each condition must precede and follow all other conditions an equal number of times

p1: easy medium hard

p2 medium hard easy

p3: hard easy medium

p4: easy hard medium

p5: hard medium easy

p6: medium easy hard

• Incomplete counterbalancing/Latin square:

P1: a1 a2 a3 a4

p2: a3 a1 a4 a2

p3: a2 a4 a1 a3

p4: a4 a3 a2 a1

But...

Treatment x Order Interaction: when how you respond to treatments depends on the order of how treatments are presented

Repeated Measures Designs

e.g., longitudinal

Mixed designs

Matched designs: matching subjects on a particular characteristic (one related to the DV)

Balance between reduction of error variance/risk of time-related effects:

eg., Does dress style affect shock reaction?

As a between groups design...

As a within-groups design...

As a matched design....