Research Methods
Outline
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The Experimental Method
Manipulation
Random Assignment
Internal and External Validity
Class Experiment
Questionnaire
The Experimental Method
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Used to establish
cause-effect relations
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Group dynamics
laboratory experiments
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Ad hoc groups
Experimental
confederates
The Experimental Method
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Example: Johnny Rocco Study
(Schachter, 1951)
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Groups to discuss a delinquent
Confederates: mode, deviate,
slider
Results: S's liked the
conforming members best. All
disliked the deviate the most.
The Experimental Method
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Two key features
1) Manipulation
2) Random assignment
Manipulation
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“Create” two or more treatment conditions
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Independent variable:
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Controlled (manipulated) by the experimenter
the hypothesized “cause’
Dependent variable:
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Measured by the experimenter (the outcome)
the outcome of “effect”
Manipulating the IV
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Lewin, Lippitt, and White leadership study
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Independent variable
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Type of leader
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Autocratic, democratic, or laissez-faire
Dependent variable
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Time spent working, amount of hostility, liking for the
leader…
Manipulation & Experimental Control
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Experiments require that everything in the
setting stay the same except for the
independent variable
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Example:
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Instructions delivered the same
Experimenters the same across conditions
Random Assignment
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Experiments must have at least 2 treatment
conditions
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Treatment (experimental) group
Control group
A given participant must be equally likely to be
assigned to any of the given groups
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Random number table
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Flip a coin
Avoiding Experimental Confounds
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Experimental control and random assignment
are designed to ensure that extraneous
variables (confounds) will not systematically
bias the study results
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Examples of experimental confounds:
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Time of day
Gender of researcher
Race of participant
Identify Key Experimental Features
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Social loafing refers to people’s tendency to slack on
group tasks. In one study on social loafing (Latane,
Williams and Harkins) 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?
Internal and External Validity
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Internal validity
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The extent to which the observed effect is caused only by
the experimental treatment condition
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The ability to draw conclusions about a causal relationship from our
data
Experiments usually high in this
External validity
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The extent to which the results can be applied to and
across different persons, settings and times
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AKA generalizability
Experiments often low in this
Generalizing From the Lab Setting
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Mundane realism
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Psychological realism
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The extent to which an experiment is similar to real-life
situations
The extent to which an experiment triggers relevant
psychological and group processes
Key point
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Lab experiments not automatically artificial
When an experiment lacks mundane realism it may be
very realistic in terms of psychological realism
Field Experiments
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Field experiments
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Experiments conducted in real-world settings
Example: Lewin, Lippitt, and White leader study
Uncommon in real-world settings
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Hard to assign people to independent variable groups
Hard to control groups so that everything is the same
except for the IV
Assess Internal & External Validity
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Does lighting affect productivity?
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Study 1:
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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).
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Study 2:
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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).
The Tradeoff
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Real life situations
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High external validity
Hard to rule out other explanations
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Low internal validity
Lab settings
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High internal validity
Often artificial and findings can’t be generalized
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Low external validity
Class Experiment
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Students randomly assigned to condition
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Heads: Stay in class and work with groups
Tails: Go outside and work alone
Task: Brainstorm on ‘uses for a brick’