PSY 380 Introduction to Social Psychology

Today's Topic:

Experimentation in Social Psychology

January 13, 1999

The correlational method

describes naturally occuring relationships

allows prediction

high generalizability

Correlation does not imply causation.

To infer causes, the experimental method must be used.

The Experimental Method

Basic components

manipulation

measurement

controlling confounding factors

An example of an experiment

"The Effects of Perceived Similarity on Liking"

Prediction: People like others who they perceive are similar to them.

Bring 50 research volunteers to the lab.

They have an informal interaction with "another participant" ("confederate").

Each person experiences one of two different situations

1. The participant meets a confederate who shares several of the same characteristics as the participant, OR

2. The participant meets a confederate who does not share any of the same characteristics.

The participant rates how well he/she liked the "other participant" on scale of 1-10

Results

Identify the components of the experiment

The manipulated variable

what did the experimenter change across the two groups?

The measured variable

what was predicted to be affected by the manipulation?

Control of confounding factors?

What other variables would you want to control (hold constant across both groups)?

The Take-Home Point

In order to design a good experiment, you need to manipulate one (or more) variables, while holding all other potentially confounding variables constant.

When everything was the same for both groups of subjects except for the variable you manipulated, then you can conclude with reasonable certainty that the differences observed between the groups was due to the manipulation.

A Field Study Example

"Status increases conformity"

Identify the main concepts involved

Operationalize the conceptual variables

Operationalization: the translation of a conceptual variable into an observable or measurable variable.

Explain the concept in terms of the operations used to produce and measure it.

Examples

Conceptual variable Operationalization

helping behavior

aggression

discrimination

attitude similarity

status

conformity

How exactly will we test the hypothesis?

Designing the procedure of our experiment is very important.

Recall our goal: Manipulation of one variable while controlling all other potentially confounding variables

This is called internal validity

What variables should we control in our study on status and conformity?

What other factors besides status might influence whether or not the participants conform?

Controlling such factors increases our internal validity

Suppose we find from our experiment that the group exposed to the high status confederate does conform more than the group exposed to the low status confederate.

What makes us so sure the groups did not differ beforehand on some important variable that can account for this difference?

Random Assignment

Random Assignment: the process by which every participant has an equal chance of taking part in any condition of an experiment.

It is extremely important that each person participating in the experiment is randomly assigned to one condition or the other.

Assures that groups are equal to begin with.

Demonstration

Random Assignment

the key component of the experimental method

differences in the personalities, backgrounds, abilities of the participants are distributed equally across conditions

people who are naturally high and low in passivity and suggestibility are equally distributed into each condition.

Now that we have achieved high internal validity, we must also consider the external validity.

external validity: the extent to which the results of a study can be generalized to other situations and to other people

Does our study really reflect the real world?

Laboratory vs. Field Experiments

Field experiments

External validity is quite high in field experiments

But in field experiments it is difficult to control confounding variables.

The researcher's dilemma

high internal validity can be achieved in "sterile laboratory conditions"

but external validity suffers in "sterile laboratory conditions"

field experiments increase external validity, but at the expense of internal validity

How to resolve this dilemma?

Develop hypotheses from observing the real world.

Test the hypothesis in controlled lab conditions

Re-test the hypothesis in field experiments

Thus, we can go "full circle" in our research, from the real world, into the lab, and back to the real world.

Your paper assignment

Design your own experiment

state hypothesis

describe procedure, IV, DV, control of other factors

predicted results

how you followed ethical guidelines

informed consent, justified use of deception, free to leave w/o penalty, full debriefing