LECTURE 11 Chapter 11 Repeated Measures / Within Subs Design 1.Control error variance = individual diff. No diff. due to sampling error! 2. Fewer subjects.

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Presentation transcript:

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

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?

Repeated Measures / Within Subs Design 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 disadvantages 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)

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

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

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

Relevant variable…eye of the beholder… weight, gender, eye color, visual acuity 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…

Single subject experimental designs: ABAB Reversal Design 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 10 episodes