Critical Thinking

1
Critical Thinking

• How could that be a coincidence?

Principle It is easier to find coincidences if
you shoot the arrow first, and draw the bulls
eye later
2
Advantages of factorial designs

• More than 1 IV can be manipulated in an
  experiment thus more than one IV can be tested
• Researcher can control a potentially confounding
  variable by building it into the design
• It produces greater precision than does an
  experiment with only one variable
• Enables the researcher to study the interactive
  effects of the IV on the DV

3
Factorial Design

• Two IV A and B
• Assume that A has 3 levels
• Assume that B has 2 levels
• There are six combinations of two IV

4
Factorial Design
IV A
A1 A2 A3
B1
IV B
B2
5
Factorial Design

• Each one of the treatment combinations is
  referred to as a cell
• Main effect influence of one IV in a factorial
  design
• Main effect for A tells us if there was a
  significant difference among the three levels
• Main effect for B tells us if there was a
  significant difference among the two levels

6
Factorial Design

• Interaction effect
• Influence of one IV has on another

7
A main effect significant
8
B main effect significant
9
Interaction significant
10
A and B significant main effects
11
Desire to interact
12
Factorial Design

• I am interested in the effects of crowding on
  behavior, emotion, and health

13
Factorial Design
Pleasantness Pleasant Unpleasant
Density Low High
14
Factorial Design
Pleasantness Pleasant Unpleasant
2.06 2.07
Density Low High
2.12 2.01
15
Factorial Design

• Higher numbers indicate greater liking of the
  experience. High density increased liking more
  than low density did when the situation was
  pleasant. However, high density decreased liking
  more than low density did when the situation was
  unpleasant

16
How to analyze a factorial design?

• When we have one IV?

ANOVA

• When we have more than one IV?

Factorial ANOVA