1. Lecture Outline
Introduction to experimental research
Introduction to correlational research
Three types of research validity
Class Activity
2. Experimental Research
Overview and Major Features
An independent variable (IV) is manipulated
A dependent variable(s) (DV) is measured
Many basic experiments consist of two levels of the independent
variable
experimental group
control group
Control over extraneous variables
holding constant
randomizing effects
A causal relationship between the independent and dependent
variables can be established
3. Basic Goal of Experimental Design
Manipulate possible values of the IV
Observe behavioral changes as indexed by values of the
DV
4. Basic Characteristics of Experimental Designs
Subjects are randomly assigned to research groups
A given participant must be equally likely to be assigned to any of the
given groups
Random number table
Flip a coin
In experimental designs, a causal relationship between the
independent and dependent variables can be established
5. Independent Variable
Differing values of the IV are called “levels”
May vary quantitatively
10 mg day
20 mg day
e.g. here are 2 levels of variable dosage
May vary qualitatively
Zoloft
Imipramine
Prozac
e.g. here are 3 levels of the variable medication type
6. •An operational definition is a clearly defined set of
procedures for measuring or manipulating the construct of
interest.
•The key to an acceptable operational definition is that the
procedure is specified precisely enough to allow replication by
others.
Examples:
quality of memory -- accuracy of recall in a certain task
depression -- Beck Depression Inventory (survey) score
arousal -- galvanic skin response (conductivity of the surface
of the skin)
Operational Definitions
7. She is a good car
salesperson
She:
1. Sells many cars
2. Points out + features
3. Is nice
4. Sells only good cars
Verbal Statement Operational Definition
Operational Definitions: Examples
8. Stress
1. Environment/Number of stressors
a. Number negative Life events
b. Number of Examinations
2. Self-report
Measurable Nervous mood
3. Behavior
a. number of fidgets/minute
b. Psychophysiological
responses elevated
Verbal Statement Operational Definition
Operational Definitions: Examples
9. Identify Key Experimental Features
Social loafing refers to people’s tendency to slack on group tasks.
In one study on social loafing college participants cheered alone,
and in groups of 2, 4, or 6 ppl. They were told to cheer as loud
as possible at specific times so researchers could determine how
much noise people made in social settings. The amount of noise
made by each participant dropped as group size increased.
1) What is the IV?
2) What is the DV?
3) Why is random assignment important here?
10. Correlational Research: Major Features
No independent variables are manipulated
Two or more variables are measured and a relationship established
Correlational research does not show causality
Don’t confuse statistics with research design
Correlation coefficients ( a statistic) can be used in correlational or experimental
research designs (although they are more commonly used in correlational designs)
12. Example of Non-Linear Relationship
Yerkes-Dodson Law
Performance
Arousal
Better
Worse
Low
High
13. Correlation Does Not Imply Causation
Causality – must demonstrate that changes in one
variable can only be due to influence of the other
variable
Directionality of Effect Problem
Third Variable Problem
16. X Y
X Y
Aggressive Behavior Viewing Violent TV
Aggressive Behavior Viewing Violent TV
Aggressive children may prefer violent programs or
Violent programs may promote aggressive behavior
Directionality of Effect Problem
22. Measurement Considerations
Variables should be measured accurately and consistently.
Accuracy
Validity
Bathroom scale gives correct weight
Consistency
Reliability
Bathroom scale gives same weight consistently
23. Evaluating Research: 3 Validities
Validity
How accurate is the information from our research?
Three validities
Construct validity
Internal validity
External validity
25. Construct Validity
The degree to which the construct can be inferred from the operational
definition of that construct
Never one perfect operationalization
Schacter and Singer (1962)
Two-factor theory of emotion:
Emotions require arousal and label
Factor 1: AROUSAL
Participants received epinephrine shots and either
informed them of side-effects or not
Factor 2: LABEL
Participants around "euphoric" or "angry“
confederate
26. How Valid are These Manipulations?
Euphoria
Confederate shoots rubber bands, plays with hula hoops and crumples up
paper and practices hook shots into wastebasket
Anger
Confederate complains about the injection, adds negative comments
about the questionnaire they are filing out and ends up ripping up the
questionnaire.
28. Internal and External Validity
Internal validity
The extent to which the observed effect is caused only by the
experimental treatment condition
The ability to draw conclusions about a causal relationship from our data
Experiments usually high in this
External validity
The extent to which the results can be applied to and across different
persons, settings and times
AKA generalizability
Experiments often low in this
29. Generalizing From the Lab Setting
Mundane realism
The extent to which an experiment is similar to real-life situations
Psychological realism
The extent to which an experiment triggers relevant psychological and
group processes
Key point
Lab experiments not automatically artificial
When an experiment lacks mundane realism it may be very realistic in
terms of psychological realism
30. Assess Internal & External Validity
Does lighting affect productivity?
Study 1:
Give people a production task in a laboratory. The
lab room is either bright or dim. Measure and
compare their productivity (how quickly and
accurately they perform the task).
Study 2:
Give employees in a well-lit office and those in a dim
office a production task. Measure and compare their
productivity (how quickly and accurately they
perform the task).
31. The Tradeoff
Real life situations
High external validity
Hard to rule out other explanations
Low internal validity
Lab settings
High internal validity
Often artificial and findings can’t be generalized
Low external validity
