Research Design

Notation: O = Observations / Measures Osubscript = measure taken on that occasion X = Treatments / Programs Rows = Groups R = Random assignment to group N = Nonequivalent groups C = Assignment by cutoff Time = moves left to right

Types of Designs

Experimental Design • probably the strongest design with respect to

internal validity.

• key to the success of the experiment is in the random assignment (achieves probabilistic equivalence).

The simplest of all experimental designs: two-group posttest-only randomized experiment.

Remember this?

Remember this?

This is an Extremely Simple Design Only One Independent Variable (Factor):

Advertising Exposure

What about a design with more than one independent variable?

Independent Variable 1 (Factor 1): Ad Color Two Levels: B&W (1) / CMYK (2) Independent Variable 2 (Factor 2): Humor in Ad Two Levels: Not Humorous (1) / Humorous (2)

Research Design Notation (Post-Test Only) = 4 Groups

R X11 O B&W / Non-humorous R X12 O B&W / Humorous R X21 O CMYK / Non-humorous R X22 O CMYK / Humorous

2 x 2 Factoral Design

Humor

B&W Non-humorous

X11

B&W Humorous

X12 C

olor

CMYK

Non-humorous X21

CMYK Humorous

X22

Understanding Factoral Design Numbering Notation

Design Factors Levels Groups 2 x 2 2 2 / 2 4 2 x 3 2 2 / 3 6 3 x 3 2 3 / 3 9

2 x 2 x 2 3 2 / 2 / 2 8 3 x 2 x 2 3 3 / 2 / 2 12

How Factoral Designs Work

Factor 1 Level 1

Factor 1 Level 2

Factor 2 Level 1

Group 1 Mean

Group 2 Mean

Mean Across

Factor 2 Level 2

Group 3 Mean

Group 4 Mean

Mean Across

Mean Down

Mean Down

No Effects (Null Outcome)

Factor 1 Level 1

Factor 1 Level 2

Factor 2 Level 1

3

3

3

Factor 2 Level 2

3

3

3

3

3

Main Effect of Factor 1

Factor 1 Level 1

Factor 1 Level 2

Factor 2 Level 1

2

4

3

Factor 2 Level 2

2

4

3

2

4

Main Effect of Factor 2

Factor 1 Level 1

Factor 1 Level 2

Factor 2 Level 1

2

2

2

Factor 2 Level 2

4

4

4

3

3

Main Effect of Each Factor

Factor 1 Level 1

Factor 1 Level 2

Factor 2 Level 1

2

4

3

Factor 2 Level 2

4

6

5

3

5

Interaction Effect (one group differs from all others)

Factor 1 Level 1

Factor 1 Level 2

Factor 2 Level 1

3

3

3

Factor 2 Level 2

3

5

4

3

4

Interaction Effect (Crossover)

Factor 1 Level 1

Factor 1 Level 2

Factor 2 Level 1

3

5

4

Factor 2 Level 2

5

3

4

4

4

Adding a Control Group

R X11 O B&W / Non-humorous R X12 O B&W / Humorous R X21 O CMYK / Non-humorous R X22 O CMYK / Humorous R O Control

2 x 2 Factoral Design with Control (not a fully-crossed design)

Incomplete Factoral Design Factor 1

Level 1 Factor 1 Level 2

Factor 2 Level 1

Group 1 Mean

Group 2 Mean

Mean Across

Factor 2 Level 2

Group 3 Mean

Group 4 Mean

Mean Across

Mean Down

Mean Down

Control Mean