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Within-Subject Design • Also called repeated-measures design • Experiment time is usually brief (< 30 minutes) • Good when the population of interest is scarce • 例如:betel nut chewer
Within-Subject Design • No need to worry about equivalent group problem • Statistically, remove the variance due to the individual difference from the nonsystematic error, increasing the probability to reject null hypothesis
SSbetween subj NO difference between treatments due to subject difference ∵ within-treatment errors include between-subject difference
Counterbalance Testing once per condition • Complete counterbalance • 2 conditions: 2!=2 orders (at least 2 participants), [1,2] [2,1] • 3 conditions : 3!=6 orders (at least 6 participants), [1,2,3] [1,3,2] [2,1,3] [2,3,1] [3,1,2] [3,2,1] • 4 conditions : 4!=24 orders (at least 24 participants) • 10 conditions : 10!=3628800 orders • GOOD for fewer conditions
Counterbalance • Many conditions (e.g., > 3): Use partial counterbalancing • Latin squares:1.each condition appears once in each raw and column; 2. Each condition precedes and follows each condition one time
Block randomization • Block randomization:當每一種情境出現的次數超過一次時,可使用此法 • In each block,condition orders are randomized • 3 conditions (A, B, C)
Block 1 Block 2 C-B-A A-C-B Block 1 Block 2 A x 3 B x 3 C x 3 A x 3 B x 3 C x 3
Block randomization • 情緒刺激(雙字詞或臉)x情緒種類(中性、恐懼或高興)x 5 repetitions (trials) • 6 (2x3) conditions, each repeats 5 times • 共2 x 3 x 5 = 30 trials • 分兩個block進行,一個block有30 trials。故實驗共有60 trials (30 trials x 2 blocks)
Block 1 Block 2 A x 5 B x 5 C x 5 D x 5 E x 5 F x 5 A x 5 B x 5 C x 5 D x 5 E x 5 F x 5
Block randomization • 可和counterbalancing搭配 • 情緒刺激(雙字詞或臉)x 情緒種類(中性、恐懼或高興)x 5 repetitions (trials) • First block: 雙字詞(15 trials = 3 x 5) • Second block: 臉(15 trials = 3 x 5) • complete counterbalance [1,2] [2,1] • 看實驗結果來判斷是否和counterbalancing搭配
臉 詞 Block 1 Block 2 A x 5 B x 5 C x 5 A x 5 B x 5 C x 5 詞 臉 Block 1 Block 2 A x 5 B x 5 C x 5 A x 5 B x 5 C x 5
Within-Subjects, Single factor • 2 levels • Lee and Aronson (1974), how do we maintain balance in a moving environment • IV: moving direction of wall and ceiling (backward or forward) • Student’s t test • ≥ 2 levels • Steele, Ball, and Runk (1997), examine the Mozart effect • IV: Listening music (control, Mozart, and soothing environment sounds)
Analyzing Single-Factor, >2 levels • F Test (analysis of variance, ANOVA變異數分析) • ≥ 2 conditions (or groups) • When 2 conditions, F = t2 • When more than 2 conditions, why not use t test?
EXAMPLE: F Test • 用t test作多重比較, 至少出現一個type I error機率 • 1 – (1 – alpha)c (C: # of paired comparisons) • 噪音程度(無,低,中,高)對記憶的影響 • C = 4!/(2!2!) = 6 • 1-(1-.05)6 = .26 (=26%!!!) • F test 同時比較多組, alpha控制在.05 • H0: μ1 = μ2 = μ3 = μ4 …
EXAMPLE: F Test • Omnibus F test • H0: μ1 = μ2 = μ3 = μ4 … • Post hoc comparisons • Paired comparisons • Control “overall” alphaat .05 • Many control methods: Bonferroni, Shaffer, Sheffet and so on
FACTORIAL DESIGNS • Simplest Factorial Design • 2 x 2 (two-by-two) factorial design • Has two independent variables, each IV has 2 levels • 4 conditions • Number of levels of first IV x Number of levels of second IV x Number of levels of third IV…
FACTORIAL DESIGNS • Interpretation of Factorial Designs (A x B) • Main effects of an independent variable:effect of A factor ONLY (regardless of B factor, average out B factor) • Interaction between the independent variables (how does effect of A factor vary with B factor?),條件機率 • A (A1, A2) x B (B1, B2) • 使用圖表讓讀者瞭解
A - B = C – D 詞頻的效果是否隨者噪音程度改變 A – C = B – D 噪音效果是否隨者詞頻程度改變