chapter 5 introduction to experimental research. chapter 5. introduction to experimental research...
TRANSCRIPT
CHAPTER 5Introduction to
Experimental Research
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
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
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
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”
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
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
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
Manipulated versus Subject Variables
• 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
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
Manipulated versus Subject Variables
• Using both manipulated and subject IVs• Bandura’s Bobo study (Box 5.2)• Manipulated type of exposure to violence
• Subject genderIndependent: Type of aggression, gender
Extraneous:Emotional arousal, Proportion of aggressor to Bobo size
Dependent:Aggression score
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)
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
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
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.