Designs

Single-factor designs: Between-subjects

Single factor designs Involve 1 IV (2 or more levels) Ex: Eyewitness memory Hypothesis: witnessing a violent event can impair memory for details just preceding the event.

- IV -DV -Results

- IV: type of movie (violent, not violent) -DV -Results

- IV: type of movie (violent, non violent) -DV: % correct recall -Results: Violent movieNon violent movie Recall4%28%

Single factor designs Within-subjects

Ex: Liking of odors Hypotheses: - An odor encountered frequently will be preferred to a novel one. - There will be no difference between a novel and a somewhat familiar odor.

IV: Type of odor (very familiar, somewhat familiar, novel) DV: Liking score on Likert scale Results: Higher liking scores for very familiar odor. No difference between somewhat familiar and novel.

Advantages Economical Excellent control over variability Increased sensitivity to find effect of IV

Problems Limited in applicability Practice and carry-over effects

Factorial designs (complex designs)

2 IVs (or more) each with at least 2 levels Factorial designs

Ex. between-subjects IVs: 1. Age = young vs. old 2. Dosage = 20 mg vs. 40 mg DV: # symptoms 2 x 2 factorial design (= 4 conditions) IV1 IV2

Ex within-subjects Longitudinal study Infants’ interactions (smiles) to their parents (mother vs. father) at 3 different ages (3, 6, 9 mos).

IVs: 1. parents = mother vs. father 2. age = 3 vs. 6 vs. 9 months DV : % smiling 2 x 3 factorial design ( = 6 conditions but only 1 group) IV1 IV2

Mixed factorial design between- and within-subjects Very frequent type of design

2 gender (male, female) x 2 topic (math, literature) – same pps tested in math and lit. # IVs: 2 (1 between and 1 within) # levels: 2 each # groups of subjects: 2 (male and female) # conditions (or cells): 4 MaleFemale Math55 Lit.55 Gender and Confidence in Math and Lit.

We have a 2 x 2 mixed factorial design

Advantages of factorial designs Economy: can examine the effects of more than 1 variable Flexibility: choose the number of IVs and of levels.

List Length Short (10 items)Long (20 items) Type of Media Study timePicturesWordsPicturesWords 5 min.XXXX 30 min.xxxX Effect of studying time and list length on memory for pictures vs. words # IVs: # levels for each IV: #conditions (cells): # groups of subjects: 3 (list length, type of media, study time) 2 for each IV 8 Depends – (1 within/2 between; 2 within/1 betw.)

We have a 2 x 2 x 2 mixed factorial design

Examples # IVs in a 4 x 2 design: How many levels in each IV: How many conditions: How many groups:

Examples # IVs in a 4 x 2 design: 2 How many levels in each IV: 4 and 2 How many conditions: 8 How many groups: don’t know

Examples # IVs in a 3 x 2 x 2 design: How many levels in each IV: How many conditions:

Examples # IVs in a 3 x 2 x 2 design: 3 How many levels in each IV: 3, 2, 2 How many conditions: 12

Examples # IVs in a 2 x 2 x 5 design: How many levels in each IV: How many conditions:

Examples # IVs in a 2 x 2 x 5 design: 3 How many levels in each IV: 2, 2, 5 How many conditions: 20

Interactions

Interaction An interaction is present when the effect of one of the IVs on the DV is not the same at all levels of the second IV.

Study on the recognition of emotional vs. neutral words in two different populations

Design 2 diagnostic category (schizophrenic, control) x 2 type of words (emotional, neutral) 2 x 2 between-subjects design 4 cells 4 groups of subjects DV: # words recalled

Hypothesis: - Schizophrenic participants will remember more neutral words than emotional ones BUT - Control participants will remember more emotional words than neutral ones.

The effect of Type of Words varies with the Type of Population Or The effect of Type of Population varies with the Type of Words

Hypothesis: - High arousal is better for simple tasks than for complex ones BUT - low arousal is better for complex tasks than high arousal. (or under low arousal there is a small diff. between simple and complex tasks)

Arousal Task complexity HighLow Simple Complex

More on interactions Hypothesis: Under success, Af.Am captain is evaluated more positively than Cauc. captain BUT Under failure, Cauc. Captain is evaluated more positively than AfAm. Captain

First IV: race of captain (AfAm, Cauc) 2 nd IV: outcome (success, failure) DV: evaluation of captain

Race of captain Condition AfAmCauc Success Failure

Race of captain Condition AfAmCauc Diff scores Success Failure Diff. scores 15485

Task Difficulty Anxiety EasyHard Low High The effect of task difficulty differs across the levels of anxiety: For low Anx., an easy task yields a better performance than a hard task, BUT for high Anx., the performance is the same for easy and hard tasks DV: mean number of tasks completed

Task Difficulty Anxiety EasyHard Low High The effect of Anxiety differs across the levels of Task difficulty: For an Easy task, Low Anxiety yields a better Performance than High Anxiety, BUT for a Hard task, Low Anxiety yields a worse performance than High Anxiety Looking it at the other way

AN INTERACTION BETWEEN ANXIETY AND TASK DIFFICULTY

The effect of task difficulty do NOT differ across levels of anxiety: For Low Anxiety, an easy task yields better performance than a hard one AND for High Anxiety, an easy task also leads to better performance than a hard one Task Difficulty Anxiety EasyHard Low High

NO INTERACTION

Main Effects of each IV Overall effect of each IV collapsed across (or averaged over) the levels of the other IV. As many main effects as there are IVs.

Distraction Small Large Y Difficulty Low High ____ Y MARGINAL MEANS

Main effects

Is there a main effect of difficulty level? YlowY high35

x x No main effect of difficulty level: Performance is similar whether difficulty level is low or high

Is there a main effect of distraction? YS YL X X

x x Main effect of distraction: Performance is better when distraction is small than when it is large No main effect of difficulty level: Performance is similar whether difficulty level is low or high XX

- No interaction because for both TV and Videogame, violent content yields more aggression than non violent -Main effect of Type of media? Yes, videogame yields more aggression -Main effect of Type of Content? Yes, violent content leads to more aggression

-Interaction because playing videogame with violent content increases aggression compared to NV games BUT watching violent TV does not increase aggression compared to watching non violent TV -Main effect of Type of media? Yes, videogame yields more aggression -Main effect of Type of Content? Yes, violent content leads to more aggression

3 factor interaction IV: –A, B, C How many main effects: –A, B, C How many interactions: –A x B –A x C –B x C –A x B x C

Do men and women recall emotional and non emotional words in the same way and how is it linked with mood?

IV: Mood (neutral, sad, happy) Word type (emotional, non emotional) Gender (female, male) DV: # words recalled