1. CHAPTER 5 Introduction to Experimental Research

2. Chapter 5. Introduction to Experimental Research Chapter Objectives
Define a manipulated independent variable and identify examples that are situational, task, and instructional variables
Distinguish between experimental and control groups
Recognize the presence of confounding variables in an experiment and understand why confounding creates serious problems for interpreting the results of an experiment

3. Chapter Objectives
Identify independent and dependent variables, given a brief description of any experiment
Distinguish between manipulated independent variables and those that are subject variables
Describe the interpretation problems that accompany the use of subject variables

4. Chapter Objectives
Recognize the factors that can reduce the statistical conclusion validity of an experiment
Distinguish between the internal and external validity of a study
Describe the various ways in which an experiment’s external validity can be reduced

5. 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”

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. The Validity of Experimental Research
Statistical conclusion validity
Proper statistical analyses and conclusions
Construct validity
Well-chosen and well-defined IVs and DVs
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)

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

14. Threats to Internal Validity
Participant problems
Subject selection: method/criterion for participation produces a confound
The Brady study  ulcers in executive monkeys
Attrition
Loss of data
Subject selection problem

15. Summary
Experimental research involves independent and dependent variable, in an effort to test the effects of the IV on the DV.
We attempt to control for confounding variables to increase the internal validity of our study.
We must consider other possible threats to internal validity as they pertain to our study.
Once we identify IVs, DVs, and threats to validity, we design a study to control those threats.