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LECTURE 11 Chapter 11

LECTURE 11 Chapter 11. Repeated Measures / Within Subs Design. Advantages. Control error variance = individual diff. No diff. due to sampling error!. 2. Fewer subjects are needed!. IV – 3 cond 20 20 20. IV – 3 cond 20. 3. Instructions given once.

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LECTURE 11 Chapter 11

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  1. LECTURE 11 Chapter 11 Repeated Measures / Within Subs Design Advantages • Control error variance = individual diff. • No diff. due to sampling error! 2. Fewer subjects are needed! IV – 3 cond 20 20 20 IV – 3 cond 20 3. Instructions given once 4. More sensitive to find effect…

  2. Statistical Analysis: • Repeated measures ANOVA • Major advantage • same participants in each condition • Sampling error (error variance)??? • Individual differences gonesville Systematic effects + error variance error variance F = If smaller denominator…bigger F ratio…bigger F??? 100/50 = 2 or 100/10 = 10…what would you prefer?

  3. Repeated Measures / Within Subs Design disadvantages • Sequence effects (2 types) • Practice Effects: growing experience • (not due to a particular condition) • a. positive: scores get better & better • b. negative: scores get worse & worse • (Swimming & coaching)  give breaks • Carryover effects: due to a particular • condition or combos…order of conditions • (drugs: 0.1, 1, 3, 10, 100 mg) • (lighting: dim, med, bright vs bright, med, dim)

  4. How to control for Sequence Effects BEST CONTROL: Random Order of Presentation: randomly vary order of conditions for each participant BETTER CONTROL: Counterbalance: systematically arrange the order of presentation so that all possible combos are presented

  5. Complete counterbalancing: all possible orders, same amount of times Calculate X! (X= # of conditions) (! = multiply all integers smaller than the # of con) Ex: (3x2x1) = n = 6 (4x3x2x1) = 24 (5x4x3x2x1) = 120

  6. Partial counterbalancing: Latin Square Design: condition only appears once in each row and once in each column

  7. Matched Design: match subs into groups based on • relevant variable likely to have an effect on the DV • Use When: • within subs not plausible (ex: surgical procedure) • Time constraints neg. impact on Subs • Ss might guess hypothesis Advantage: no worry about sequence effects… Relevant variable…eye of the beholder… weight, gender, eye color, visual acuity

  8. Single subject experimental designs: ABAB Reversal Design 10 episodes Stan (brain injury) - hoarding cig butts, pieces of dust, Food, socks, underwear in pockets Time out: 10 min in quiet area + reinforcement for good behavior

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