Post on 31-Dec-2015
Literature Review PaperLiterature Review Paper
• Use a summary narrative form
• Assignment sheet http://commfaculty.fullerton.edu/jreinard/sample_papers.htm
• Outline format essential
Agenda for This Unit
• Experimental Design
• Causal Reasoning in Experiments
• Notation
• Factorial Designs
• Main Effects
• Interaction Effects
Experimental Design
Defined: a study of the effects of variables manipulated by a researcher in a situation in which all other variables are controlled, completed for the purpose of establishing causal relationships
Experimental Design• Distinguishing Carefully Designed
Studies from Experiments
• Manipulation of Variables
• Cause-effect Conclusions
Finding True Causes in Experiments
• The Challenge of Control
• A Case Study
Notation
O -
observation
X -
experimental variable
R -
randomization
Designs
• Reading Designs
• Pre-Experimental vs. True Experimental Designs
Randomization
• controlling for extraneous variables
• random assignment
• random selection
Comparing Designs
Internal Validity
Defined: the degree to which the researcher can make an unequivocal statement of experimental effect
Sources
Mnemonic device:
He said my tush is sagging extra inches.
External Validity
Defined: the degree to which research findings can be generalized to other similar circumstances
Sources
Other Sources of Invalidity
• Law of the Instrument
• Experimenter Effects (Demand Characteristics)
• Ignoring Initial Differences between Control and Experimental Groups
Factorial Designs
Defined: experimental designs using more than one independent variable
One Factor DesignsX1- +
A Two Factor Design
A 2 x 2 Design
X1- +
- +
X2
A 3 x 2 DesignX1
- +
X2
LOW MO HI
A Three Factor Design
X1- +
- +
X2
- +
X3
The Relationship Between Factorial and Simple Designs
X1- +
- +
X2
The Relationship Between Factorial and Simple Designs
X1- +
- +
X2
R X OR OR X OR O
R X OR O
R X OR O
Identification of Offset Control Groups
X1- +
- +
X2
R X OR OR X OR O
R X OR O
R X OR O
Identification of Offset Control Groups
X1- +
- +
X2
R X O
R X OR O
R O
R X OR OR X OR O
Designs in Which Control Groups are Included
X1- +
- +
X2
R X O
R X OR O
R X OR OR X OR O
Main Effects
Defined: dependent variable effects from independent variables separately
A Main Effect Example
X1- +
- +
X2
5040
3020
Amount of Attitude Change Advocated
Source Character
A Main Effect Example
X1- +
- +
X2
5040
3020
30 40
Amount of Attitude Change Advocated
Source Character
A Main Effect Example
X1- +
- +
X2
5040
3020 25
45
30 40
Amount of Attitude Change Advocated
Source Character
Diagrams of Main Effects
20
15
10
5
Men Women
Variable 1
D.V.:touching
Diagrams of Main Effects
20
15
10
5
Men Women
Variable 1
D.V.:touching
Diagrams of Main Effects
50
40
30
20
Low High
Variable 1
Amount of Attitude Change Advocated
D.V.:AttitudeChange
Diagrams of Main Effects
50
40
30
20
Low High
Variable 1
Variable 2 (Low)
Amount of Attitude Change Advocated
Source Character
D.V.:AttitudeChange
Diagrams of Main Effects
50
40
30
20
Low High
Variable 1
Variable 2 (High)
Variable 2 (Low)
Amount of Attitude Change Advocated
Source Character
D.V.:AttitudeChange
Effects X1- +
- +
X2
19 9
2111
Effects X1- +
- +
X2
19 9
2111 16
14
Effects X1- +
- +
X2
19 9
2111 16
14
2010
Diagrams of Main Effects
20
15
10
5
Low High
Variable 1
Diagrams of Main Effects
20
15
10
5
Low High
Variable 1
Variable 2 (Low)
Diagrams of Main Effects
20
15
10
5
Low High
Variable 1
Variable 2 (Low)
Variable 2 (High)
Interaction EffectsDefined: dependent variable effects from
independent variables taken together
Forms: Ordinal
(in the same direction as the main effects of variables involved)
Disordinal
(not in the same direction as the main effects of
the variables involved)
An Interaction Effect ExampleX1- +
- +
X2
5020
2020
An Interaction Effect ExampleX1- +
- +
X2
5020
2020 20
35
An Interaction Effect ExampleX1- +
- +
X2
5020
2020 20
35
20 35
Diagram of the Interaction Effect
50
40
30
20
Low High
Variable 1
Diagram of the Interaction Effect
50
40
30
20
Low High
Variable 1
Variable 2 (Low)
Diagram of the Interaction Effect
50
40
30
20
Low High
Variable 1
Variable 2 (High)
Variable 2 (Low)
Another Interaction Effect Example
X1- +
- +
X2
2040
4020
Sex of Clinician
Male FemaleType of Stuttering: Clonic
Blocking
Another Interaction Effect Example
X1- +
- +
X2
2040
4020
Sex of Clinician
Male FemaleType of Stuttering: Clonic
Blocking
30 30
Another Interaction Effect Example
X1- +
- +
X2
2040
4020
Sex of Clinician
Male FemaleType of Stuttering: Clonic
Blocking
30
30
30 30
Diagram of the Interaction Effect
40
30
20
10
Low High
Variable 1 Male Female
Sex of Clinician
Diagram of the Interaction Effect
40
30
20
10
Low High
Variable 1
Variable 2 (Low)
Male Female
Sex of Clinician
Type of Stuttering:
Clonic
Diagram of the Interaction Effect
40
30
20
10
Low High
Variable 1
Variable 2 (Low)
Variable 2 (High)
Male Female
Sex of Clinician
Type of Stuttering:
Clonic
Blocking
Interpreting Ordinal Interactions
• acceptable to look at the independent variables separately
• permissible to interpret main effects for independent variables involved in the interaction
Interpreting Disordinal Interactions
• must look at both independent variables together
• not permissible to interpret main effects for independent variables involved in the interaction
OK to Interpret Main Effects
50
40
30
20
Low High
Variable 1
Variable 2 (High)
Variable 2 (Low)
Not OK to Interpret Main Effects
40
30
20
10
Low High
Variable 1
Variable 2 (Low)
Variable 2 (High)
Effects: Example 1
20
15
10
5
Low High
Variable 2
Effects: Example 1
20
15
10
5
Low High
Variable 2
Variable 1 (Low)
Effects: Example 1
20
15
10
5
Low High
Variable 2
Variable 1(High)
Variable 1 (Low)
20
15
10
5
Low High
Variable 2
Effects: Example 2
20
15
10
5
Low High
Variable 2
Effects: Example 2
Variable 1 (Low)
20
15
10
5
Low High
Variable 2
Effects: Example 2
Variable 1 (High)
Variable 1 (Low)