1. CHAPTER 5 Introduction to Experimental Research

2. The meaning of Experiment
Experiment: a systematic research study in which the investigator directly manipulates some factor, holds all other factors constant, and observes the results of the variation.(contrast with correlation)
“investigating the effect of X on Y”

3. Essential Features of Experimental Research
Establishing independent variables (IVs)
Manipulated IVs : must have minimum of 2 levels
Situational: environmental features
Task: different problems to solve
Instructional: performing tasks in different ways
Experimental groups
given treatment
Research Example  given a golf ball and told it was a “lucky” ball
Control groups
treatment withheld
Research Example  given a golf ball and not told it was a “lucky” ball

4. Essential Features of Experimental Research
Controlling extraneous variables: variables which are not of interest to the researcher but which might influence the behavior being studied if not controlled for properly.
Confounds
Any uncontrolled extraneous variable
Covaries with the IV; results could be due to IV or to confound
Distributed practice example

5. Essential Features of Experimental Research
Measuring dependent variables (DVs)
DVs are any behaviors measured in an experiment
Review scales of measurement (Ch. 4)!
Problems:
Ceiling effects
task is too easy, all scores very high, disguising any differences
Floor effects
Task too difficult, all scores very low, disguising any differences
Solution:
Task of moderate difficulty, determined through pilot testing

6. Manipulated versus Subject Variables
Already-existing attributes of subjects in a study
Examples  gender, age, personality characteristic
Anxiety example
As a manipulated variable  induce different degrees of anxiety in participants
As a subject variable  choose participants who have different degrees of their typical anxiety

7. Manipulated versus Subject Variables
Cannot draw certain conclusions when using subject variables
With a manipulated IV
Assuming no confounds  IV causes DV
With a subject IV
Groups may differ in several ways  IV cannot be said to cause DV
All that can be said  the groups differ from each other

8. Manipulated versus Subject Variables
Using both manipulated and subject IVs
Bandura’s Bobo study (Box 5.2)
Manipulated  type of exposure to violence
Subject  gender
Independent:
Type of aggression, gender
Extraneous:
Emotional arousal,
Proportion of aggressor
to Bobo size
Dependent:
Aggression score

9. The Validity of Experimental Research
External validity: the degree to which research findings generalize beyond the specific context being studied (subject pools, the college sophomore problem, the male problem)
Internal validity- methodologically sound and confound-free (confidence that IV is directly responsible for results)

10. Threats to Internal Validity
Studies extending over time (may have pretests)
Example: Test-anxiety reduction
History
Maturation
Regression to the mean
Testing and instrumentation- practice effects, change in measurement instruments/coders
Importance of using a control group

11. Threats to Internal Validity
Participant problems
Subject selection: method/criterion for participation produces a confound
Attrition
Loss of data
Subject selection problem

12. Exam 1: Types of Questions
Validity of a scale is defined as its:
ability to produce replicable results
ability to measure what it’s supposed to measure
ability to express meaningful ratios
ability to produce the same value for every measurement

13. Exam 1: Types of Questions
You purchase a scale with which to weigh your pet cat. You weigh your cat several times and each time the scale reads 2lbs. However, you have a fairly old and large cat and you know (as per your vet’s scale) that he weights at least 15lbs. Your scale is:
Valid but not reliable
Reliable but not valid
Both valid and reliable
Neither valid nor reliable

14. Exam 1: Types of Questions
Give two examples of unethical behavior in any well- known studies (you can refer to those which we have discussed in class or which appear in the book).