Repeated Measures (WS) Designs

1. Repeated Measures (WS) Designs • Definition • Benefits and “hazards” • State of Practice (SOP) effects • Control by balancing • Pre-test practice trials • Designs • Complete • Incomplete practice High Skill Low Trials

2. Designs—Complete Balance SOP effects across conditions/ within subjects • Block randomization • 6 conditions (A,B,C,D,E,F) • If each participant tested 6 Xs in each condition • 6 blocks (stage) needed • Random arrangement w/in block       BCEDAF/AEBFDC/EFDCAB/ABCDEF/DFEABC/AFDCBE

3. Designs—Complete, cont. • To ID SOP effects, compare for each stage: w/w/w/w/w/ If =, no SOP effect

4. Designs—Complete, cont. • ABBA counterbalancing • Two conditions • Each subject tested multiples of 2 for each condition • If each subject tested 4 Xs in each condition, 4 stages needed     AB / BA / AB / BA Stage

5. Designs—Complete, cont. • To ID SOP effects, compare for each stage: w/w/w/ If =, no SOP effect • Nonlinear practice effects • Anticipation effects

6. Designs—Incomplete Balance SOP effects across subjects • All possible orders (permutations) • Identify all possible orders • Formula: nP = n! = n x n–1 x n–2 x … x n– (n–1), where n = number of conditions • E.g., if n = 4, nP = 4! = 4 x 3 x 2 x 1 = 24 • If n = 5? • If n = 3 (A,B,C), nP = 3! = 3 x 3 x 1 = 6,       ABC/ACB/BAC/BCA/CAB/CBA Stage • Randomly assign participants to different orders

7. Designs—Incomplete, cont. • To ID SOP effects, compare for each stage: w/w/w/w/w/ If =, no SOP effect

8. Designs—Incomplete, cont. Balance SOP effects across subjects • Selected orders • Latin square • Use when number of conditions is even • Number of conditions = number of orders = number of rows (R) in the Latin square • Assign a number to each condition

9. Designs—Incomplete, cont. Balance SOP effects across subjects • Selected orders • Latin square, cont. • Follow rules for rows of conditions • R1 rule: 1, 2, N, 3, N-1, 4, N-2, 5, etc. • R2 rule: Add 1 to each number in R1, and N + 1 = 1 • R3 rule: Same as R2 rule, up to last row

10. Designs—Incomplete, cont. • Each condition at each ordinal position at least once (_) • Each condition precedes and follows each other condition at least once • Each subject randomly assigned to only 1 row • Each row used same number of times as other rows Latin square: if 6 conditions, 6 orders = 6 rows R1 1 2 6 3 5 4 R2 2 3 1 4 6 5 R3 3 4 2 5 1 6 R4 4 5 3 6 2 1 R5 5 6 4 1 3 2 R6 6 1 5 2 4 3 Stage

11. Designs—Incomplete, cont. Balance SOP effects across subjects • Selected orders • Rotation of random starting order • Use when number of conditions is odd • Systematic rotation of conditions • Follow rules for rows of conditions • R1 rule: randomly order conditions (e.g., C,E,B,D,A, if 5) • R2 to Rn rule: move R1 conditions one position to the left, with the first condition in the row looping to the end of the row

12. Designs—Incomplete, cont. Rotation of random starting order for 5 conditions R1 C E B D A R2 E B D A C R3 B D A C E R4 D A C E B R5 A C E B D Stage • Each condition at each ordinal position once (_) • Each subject randomly assigned to only 1 row • Each subject experiences conditions in different order

13. Special Design Problems • Irreversible tasks: • A then B; not B then A • You can surprise someone only once! • Differential transfer • Learning • Fatigue • Habituation; reduced responsiveness • Contrasts • Adaptation