1. The Experimental Method in Psychology

2. Experimentation Experiment:
a research method in which an investigator manipulates one or more factors (variables) to observe the effect on some behavior or mental process (the dependent variable).

3. Experimentation Experiment: Can isolate cause and effect
Control of factors
Manipulation of the factor of interest (experimental group)
Hold constant factors (control group)

4. Experimentation Random assignment:
Participants are assigned to groups by chance, thus minimizing any differences between those assigned to the different groups.
Eliminates alternative explanations
Different from random sample

5. Experimentation Blind assignment (un-informed) Single-Blind Procedure
Participants do not know which group they are assigned to
Double-Blind Procedure
Neither participants nor the research staff know which group the participants are assigned to.

6. Experimentation Placebo effect:
Experimental results that are caused by expectations alone; any effect on behavior caused by the administration of an inert substance or condition

7. Experimentation Independent and Dependent Variables
Independent Variable (IV):
The experimental factor that is manipulated; the variable whose effect is being studied.
Dependent Variable (DV):
What is being measured. In other words, the variable that may change in response to the IV

8. Experimentation Independent and Dependent Variables
Confounding Variable:
A factor other than the independent variable that might produce an effect on the experiment

9. Experimental Design Question:
Do children who are breast-fed as infants grow up to be smarter than those fed on a bottle?

10. Experimental Design Hypothesis: Population: all children
Children who are breast-fed as infants score higher on intelligence tests than those who are bottle fed.
Population: all children

11. Experimental Design

12. Experimental Design

13. Experimental Design

14. Experimental Design

15. Comparing Research Methods
Basic Purpose
How conducted
What is manipulated
Descriptive
To observe and record behavior
Case studies, surveys, naturalistic observation
Nothing is “changed”

16. Comparing Research Methods
Basic Purpose
How conducted
What is manipulated
Correlational
To detect naturally occurring relationships
(assess how well one variable predicts another)
Computing statistical associations
Nothing is manipulated

17. Comparing Research Methods
Basic Purpose
How conducted
What is manipulated
Experimental
To explore cause and effect
Manipulate one or more variables
Use random assignment to eliminate preexisting conditions
The independent variable(s)