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 movie Non violent

movie

Recall 4% 28%

Single factor designsWithin-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 designbetween- 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

Male Female

Math 5 5

Lit. 5 5

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 time Pictures Words Pictures Words

5 min. X X X X

30 min. x x x X

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.

Type of words

Population Emotional Neutral

Schizophrenic 5 13 9

Control 14 7 10.5

9.5 10

XXX

Y

Y

Type of words

Population Emotional Neutral

Schizophrenic 5 13 9

Control 14 7 10.5

9.5 10

Y

Y

The effect of Type of Words varies with the Type of PopulationOr 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

High Low

Simple 50 35 42.5

Complex 10 25 17.5

30 30

Y

Y

0

10

20

30

40

50

60

simple complex

Task

mea

n #

of ta

sks

corr

Arousal high

Arousal low

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)• 2nd IV: outcome (success, failure)

• DV: evaluation of captain

Race of captain

Condition AfAm Cauc

Success 309.6 280.6 295.1

Failure 155.3 196.1 175.7

232.45 238.35

Y

Y

Race of captain

Condition AfAm Cauc Diff scores

Success 309.6 280.6 28.7

Failure 155.3 196.1 40.8

Diff. scores 154 85

100

150

200

250

300

350

black white

success

failure

100

150

200

250

300

350

success failure

black

white

Task Difficulty

Anxiety Easy Hard

Low 5.55 1.19 3.37

High 3.34 3.34 3.34

4.45 2.26

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 Easy Hard

Low 5.55 1.19 3.37

High 3.34 3.34 3.34

4.45 2.26

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

0

1

2

3

4

5

6

Low anxiety High anxiety

easy

hard

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 Easy Hard

Low 4.25 1.10 2.67

High 6.25 3.10 4.7

5.25 2.10

0

1

2

3

4

5

6

7

low anxiety high anxiety

easy

hard

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 YDifficulty

Low 40 30 35High 55 15 35

____ ____Y 47.5 22.5

MARGINAL MEANS

Main effects

0

10

20

30

40

50

60

low diff high diff

Diffi culty level

small

large

Is there a main effect of difficulty level?

0

10

20

30

40

50

60

low diff high diff

Diffi culty level

small

large

Ylow Y high3535

0

10

20

30

40

50

60

low diff high diff

Diffi culty level

small

large

xxNo main effect of difficulty level:Performance is similar whether difficulty level is low or high

Is there a main effect of distraction?

0

10

20

30

40

50

60

low diff high diff

Diffi culty level

small

large

YS

YL

X

X

47.5

22.5

0

10

20

30

40

50

60

low diff high diff

Diffi culty level

small

large

x

x

Main effect of distraction: Performance is better whendistraction is small than whenit is large

No main effect of difficulty level: Performance is similar whether difficulty level is lowor high

X X

TV Videogame0

0.51

1.52

2.53

3.54

4.55

Violent Non Violent

Type of Media

# a

gg

res

siv

e r

es

po

ns

es

- 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

TV Videogame0

0.51

1.52

2.53

3.54

4.55

ViolentNon Violent

Type of media

# a

gg

res

siv

e

res

po

ns

es

- Interaction because playing videogame with violent content increasesaggression compared to NV games BUT watching violent TV doesnot 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