Experiments aim to determine causal relationships between variables by manipulating one variable and observing its effects. They have advantages like determining causality and direction of influence but disadvantages like artificial conditions and requiring large numbers. True experiments use control and treatment groups, with subjects randomly assigned to determine if a variable A causes an outcome B. More sophisticated designs like the Solomon four-group control for threats to validity by adding multiple pre and post-tests across several groups. Experiments allow isolating the effect of specific variables but rarely mimic real-life conditions.

1. Introducing Communication Research 2e © 2014 SAGE Publications
Chapter Ten
Experiments: Researching Cause
and Effect

2. Key Concepts
• The basic experimental concept –
“let’s do something and see what happens”.
• Experimental designs can determine whether
variables have a causal relationship
• More sophisticated designs use experimental
groups and control groups, and random
assignment of subjects into groups.
Introducing Communication Research 2e © 2014 SAGE Publications

3. Experiment Advantages &
Disadvantages
Advantages Disadvantages
Determine causal relationships. Artificiality of experimental
conditions.
Determine direction of
causality.
Questionable validity.
Determine relative influence of
variables.
May involve ethical issues such
as deception.
Demonstrate influence of one
variable on another.
May require large numbers of
people.
Control over research
conditions.
May be time-consuming.
Introducing Communication Research 2e © 2014 SAGE Publications

4. Why Experiments?
• Correlation is not causality
• Correlation is not causality
• Correlation is not causality
• Correlation is not causality
• Surveys show correlation only.
• Experiments can assess causality.
Introducing Communication Research 2e © 2014 SAGE Publications

5. The Causality Question:
Did A cause B?
To show that A caused B, we must show-
• Time order -
▫ A must precede B.
• Meaningful co-variance -
▫ B must change as A changes.
• Non-spuriousness -
▫ Nothing except A must be influencing B.
Introducing Communication Research 2e © 2014 SAGE Publications

6. The Basic Experimental Design
Group A Group B
Treatment X
Group A results Group B results
•Do group results differ?
•If so treatment X explains it (maybe).
Introducing Communication Research 2e © 2014 SAGE Publications

7. Experiments: Low Level of Control
• Low Control -
Field or natural experiments
• Single Group, post-test -
x O1
• One Group, pre-test, post-test -
O1 x O2
Introducing Communication Research 2e © 2014 SAGE Publications

8. Experiments: Medium Level of
Control
Two groups, pre-test, post-test -
(Treatment group) O1 x O2
(Control group) O1 O2
Introducing Communication Research 2e © 2014 SAGE Publications

9. Experiments: High Level of Control
Two groups, randomized, pre-test,
post-test -
(Randomized, treatment) O1 x O2
(Randomized, control) O1 O2
Introducing Communication Research 2e © 2014 SAGE Publications

10. Experiments: High Level of Control.
Solomon Four Group Design.
Group 1 O1 x O2
Group 2 O1 O2
Group 3 x O2
Group 4 O2
Introducing Communication Research 2e © 2014 SAGE Publications

11. Solomon Four-Group Design:
Example.
Before
Program
After
Program
Random
Group 1
First survey Program Second
survey
Random
Group 2
First survey Second
survey
Random
Group 3
No survey Program First survey
Random
Group 4
No survey First survey
Introducing Communication Research 2e © 2014 SAGE Publications

12. Chapter Summary
Experiments –
• Range from simple observation to sophisticated factorial
designs.
• Expose participants to controlled conditions.
• Can isolate the effect of specific variables.
• Can determine causal relationships among variables.
• Good design requires random assignment to groups.
• Experimental conditions rarely resemble real-life
conditions.
• To assess causality requires sophisticated designs such
as the Solomon Four-Group.
Introducing Communication Research 2e © 2014 SAGE Publications

13. Vocabulary Review
Introducing Communication Research 2e © 2014 SAGE Publications

14. Web Resource
Web Center for Social Research Methods -
http://www.socialresearchmethods.net
Provides an overview of social research methods,
including experimental design.
Introducing Communication Research 2e © 2014 SAGE Publications