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’