Research Methods Outline The Experimental Method Manipulation Random Assignment Internal and...
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Research MethodsOutline The Experimental Method Manipulation Random Assignment Internal and External Validity Class Experiment Questionnaire
The Experimental Method Used to establish
cause-effect relations
Group dynamics laboratory experiments Ad hoc groups Experimental
confederates
The Experimental Method
Example: Johnny Rocco Study (Schachter, 1951)
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 Two key features
1) Manipulation
2) Random assignment
Manipulation “Create” two or more treatment conditions
Independent variable: Controlled (manipulated) by the experimenter the hypothesized “cause’
Dependent variable: Measured by the experimenter (the outcome) the outcome of “effect”
Lewin, Lippitt, and White leadership study Independent variable
Type of leader Autocratic, democratic, or laissez-faire
Dependent variable Time spent working, amount of hostility, liking for
the leader…
Manipulating the IV
Manipulation & Experimental Control Experiments require that everything in the
setting stay the same except for the independent variable Example:
Instructions delivered the same Experimenters the same across conditions
Random Assignment
Experiments must have at least 2 treatment conditions Treatment (experimental) group Control group
A given participant must be equally likely to be assigned to any of the given groups Random number table Flip a coin
Avoiding Experimental Confounds Experimental control and random assignment
are designed to ensure that extraneous variables (confounds) will not systematically bias the study results Examples of experimental confounds:
Time of day Gender of researcher Race of participant
Identify Key Experimental Features 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 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
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
Field Experiments Field experiments
Experiments conducted in real-world settings Example: Lewin, Lippitt, and White leader study Uncommon in real-world settings
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 Does lighting affect productivity?
Study 1: 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).
Study 2: 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 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
Class Experiment Students randomly assigned to condition
Heads: Stay in class and work with groups Tails: Go outside and work alone
Task: Brainstorm on ‘uses for a brick’