Lecture Outline One-way Designs Factorial Designs Main effects Interactions
One-Way Designs One-way refers to one independent variable Two groups design The simplest one-way design One IV with 2 levels Foot-in-the-door technique Get person to consent to small task first, then ask for larger task EXAMPLE: Freedman & Fraser (1966) Went door to door Small request: Sign petition Large request: Huge, ugly sign on lawn Experimental group= small then large Control group = large request only
More than two levels… Several reasons you may want more than 2 levels of one IV A) 2 levels cannot provide much information about the exact relationship between IV and DV B) 2 levels cannot detect curvilinear relationships C) May be interested in more than 2 groups
A) Lack of Precise Information Motivation and performance on a motor task 2 levels of reward $0 $4 AMOUNT OF REWARD PERFORMANCE 100 90 80 70 50 60
A) Lack of Precise Information Increased to five levels Positive monotonic relationship $1$2$3 $0 $4 AMOUNT OF REWARD PERFORMANCE 100 90 80 70 50 60
B) Curvilinear relationships Nonmonotonic Increases in the value of one variable are accompanied by increases and decreases in values of another Fear and attitude change. Level 1Level 2Level 3 Low High DEPENDENT VARIABLE
C) Interested in More Than Two Things Effects of animal companionship on nursing home residents 2 group design: Dog / No Dog More than 2 groups Dog, Bird, Cat, No animal Stress reducing techniques (Bruning & Frew, 87) 4 group design Exercise, management skills training, medication, control All 3 techniques decreased blood pressure and pulse
Increasing the IVs: Factorial Designs Factorial designs More than one independent variable (or factor) Determining the number of conditions 2 x 3 6 conditions 3 x 3 9 conditions 2 x 2 x 2 8 conditions Number of levels of first IV Number of levels of second IV Number of levels of third IV X X
A 2 x 2 Design Head movement and persuasive arguments Participants listened to a persuasive argument while moving their head Independent variables Persuasive argument: Tuition increase or tuition decrease Head movement: Nod head or shake head Conditions? 2 x 2 = 4
A 2 x 2 Design Tuition decrease- Nodding Tuition increase- Nodding Tuition decrease- Shaking Tuition increase- Shaking Persuasive Argument Movement of Head Nodding Shaking Tuition decreaseTuition increase
Main Effects Effect each variable has by itself DV: Willingness to accept increases in tuition Persuasive Argument Head Movement DecreaseIncrease Nodding400630 Shaking485465
Main Effect for Head Movement Persuasive Argument Head Movement IncreaseDecreaseOverall means Nodding400630515 Shaking485465475
Main Effect for Type of Argument Persuasive Argument Head Movement IncreaseDecrease Nodding400630 Shaking485465 Overall means442.5547.5
Both Main Effects Persuasive Argument Head Movement IncreaseDecreaseOverall means Nodding400630515 Shaking485465475 Overall means442.5547.5
Interactions The effect of one independent variable depends on the level of the other There is an interaction in the persuasive argument study The effect of the type of argument is different depending on whether the person is nodding or shaking their head Let’s take a closer look
Interactions We can look at the data to detect the interaction YUCK!! Persuasive Argument Head Movement DecreaseIncrease Nodding400630 Shaking485465
Interactions Ordinal (spreading) interaction IV1 has an effect under one condition of IV2 but less of an effect under the other condition of IV2. Disordinal (crossover) interaction There are no main effects of either IV The effects of each IV are opposite at different levels of the other IV
Ordinal Interaction IV1 has an effect under one condition of IV2 but less of an effect under the other condition of IV2.
Another Ordinal Interaction IV1 has an effect under one condition of IV2 but less of an effect under the other condition of IV2.
Disordinal Interaction There are no main effects of the IVs The effects of each IV are opposite at different levels of the other IV Mood during LEARNING
Concept Check A professor randomly assigns students to one of four conditions: Learn words in the morning and drink 2 cups of coffee Learn words in the afternoon and drink 2 cups of coffee Learn words in the morning and drink no coffee Learn words in the afternoon and drink no coffee What are the main effects and the interactions in this design? What questions would you ask to evaluate these effects?
Concept Check Main effect 1: Coffee factor Are there any differences in students who received coffee compared to those who didn’t? Main effect 2: Time of day factor Are there any differences in students who learned the words in the morning vs afternoon? Interaction: Does the effect of coffee depend on the time of day? Coffee might enhance performance in the morning but impair performance in the afternoon.
No main effect of A or B, no interaction Violent TV ThreatA1A2 B120 B220 Provocations - Main Effects & Interactions
Main effect of A, no main effect of B and no interaction Violent TV ThreatA1A2 B1204030 B2204030 2040 Provocations -
Main effect of B, no main effect of A and no interaction Violent TV ThreatA1A2 B120 B240 30 Provocations -
Main effect of A and B, no interaction Violent TV ThreatA1A2 B102010 B2204030 1030 Provocations -
No main effect of A or B; interaction Violent TV ThreatA1A2 B1402030 B2204030 Provocations -
Main effect of A, no main effect of B; interaction Violent TV ThreatA1A2 B140020 B220 3010 Provocations
Main effect of B, no main effect of A; interaction Violent TV ThreatA1A2 B120010 B2204030 20 Provocations
Main effect of A and B; interaction Violent TV ThreatA1A2 B120 B2204030 2030 Provocations -
Hands on Activities Design Identification Outcomes of Factorial Designs