CHAPTER 5 Introduction to Experimental Research

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 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  gender Independent: Type of aggression, gender Extraneous: Emotional arousal, Proportion of aggressor to Bobo size Dependent: Aggression score

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)

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

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

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

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

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).