1. Chapter 9: Conducting Experiments

2. Selecting Research Participants
Most research projects involving sampling research participants from a population of interest.
Use probability sampling when it is important to
describe the population
- Scientific polls

3. Selecting Research Participants
A great deal of research is interested in testing hypotheses about behavior.
Participants may be found in the easiest way possible using haphazard or “convenience” sampling methods.
Generalization of results
- Sample sizes needed

4. Manipulating the Independent Variable
To manipulate an independent variable
Turn a conceptual variable into a set of operations
(operational definition)
- Setting the stage
1. Provide informed consent information
2. Explain why the experiment is being
conducted

5. Manipulating the Independent Variable (con’t)
Types of manipulations
Straightforward manipulations
Staged manipulations

6. Manipulating the Independent Variable (con’t)
Straightforward manipulations
Written instructions
Verbal material
Visual material

7. Manipulating the Independent Variable (con’t)
Staged manipulations
Often employ confederates
Events are staged or manipulated to:
1. Create some psychological state
2. Simulate some situation that occurs in the
real world

8. Manipulating the Independent Variable (con’t)
Strength of the manipulation

9. Manipulating the Independent Variable (con’t)
Importance of a strong manipulation
Rare situations
Ethics
Importance of a manipulation check

10. Manipulating the Independent Variable (con’t)
Cost of the manipulation
Participants run individually versus groups
Straightforward versus staged manipulations

11. Measuring the Dependent Variable
Types of measures
Self-report measures
Behavioral measures
Physiological measures

12. Measuring the Dependent Variable (con’t)
Sensitivity of the dependent variable
Ceiling effect
Floor effect

13. Measuring the Dependent Variable (con’t)
Multiple measures
Measure more than one dependent variable
- A variable can be measured a variety of ways.
- If the IV has the same effect on several measures
of the same dependent variable, confidence in the
results increases
** Question of order arises………..

14. Measuring the Dependent Variable (con’t)
Cost of measures
Ethics

15. Additional Controls Controlling for participant expectations
Demand characteristics – use deception
Cover story
Filler items
- Ask participants their perceptions about the purpose of the study

16. Additional Controls (con’t)
Placebo groups
Single-blind experiment
Placebo effect
Balanced placebo design
Placebo control groups and ethical considerations

17. Additional Controls (con’t)
Controlling for experimenter expectations
Experimenter bias
Research on expectancy effects
Clever Hans
Teacher expectancy (Rosenthal & Jacobsen, 1968)

18. Additional Controls (con’t)
Solutions to the experimenter expectancy problem
Experimenter training
Run all conditions simultaneous
Automate the procedures
Double-blind study

19. Additional Considerations
Research proposals
Pilot studies
Manipulation checks
Debriefing

20. Communicating Research to Others
After the data have been collected, analyzed, and interpreted, communicate the findings to others
Write a report first and then communicate
1. Professional meetings
2. Journal articles

21. The End