Experimental Methods

Experiments in Psychology

One of the most widely used methods in the study of behavior

Goal is to establish a cause and effect relationship between two

variables

Performed under highly controlled conditions

Experiment is an example of quantitative research – it generates

numerical data

Can be statistically tested to rule out the role of chance in results

Does noise affect one’s ability

to recall information?

• Aim of study – will one variable (noise) has an effect

on another variable (recall or information)

• Independent Variable (IV) – causes a change in

another variable, it is manipulated by researcher

• Dependent Variable (DV) – variable that is measured

after the manipulation of the IV

Operationalizing Variables

• The experiment must be written in a way that it is clear

WHAT is being measured. Here, noise is the

independent variable

– It could be operationalized as high music at volume

35

• The number of words remembered would be the DV

– It could be operationalized as words remembered

from a list of 20 words

Apply your Knowledge

Operationalize your variables by considering each of the following

descriptions and deciding whether it is an example of aggression or

not.

Write a well-worded definition of aggression.

1. Two men fight over a parking place

2. A football player kicks the ball into the goal

3. Two girls give a boy the “silent treatment” on the playground

4. A man kicks the back of his car when it will not start

5. Three students have a heated debate about whether global warming

is happening

Formalize the aim – Researcher forms an experimental hypothesis

• Researcher predicts the relationship between the IV and the

DV – what we expect will come out of the manipulation of IV

• In this case there will be 2 conditions:

– Participants recall words in the quiet

– Participants recall words with loud noise

the quiet condition is called the CONTROL CONDITION

so that we can see if there is a difference

Make up an experimental hypothesis

for this study

How About

Noise will decrease the number of words that an

individual is able to recall from a list of words.

The IV (noise) is predicted to have an effect on the

DV (recall)

More Kinds of Hypothesis

• In Experimental Research you need a NULL

HYPOTHESIS and an EXPERIMENTAL HYPOTHESIS

• A null hypothesis: Noise has no effect on an

individual’s ability to recall a list of words

• Remember, you can never prove anything! You can

only disprove.

A researchers goal:

• Refute the null hypothesis (that sound makes no

difference in recall)

• Or accept the null hypothesis

• We can accept the experimental hypothesis only

if we demonstrate the effect was due to the

manipulation of the IV

Identify the IV and DV in each of the experimental hypothesis:

1. People are more likely to make a risky decision

when they are in a group than when they are alone.

2. An increase in carbohydrates decreases one’s

ability to concentrate.

3. People will react more quickly to an auditory

stimulus than a visual stimulus.

4. Lack of sleep will affect learning new words

negatively.

Kinds of Experiments

• Laboratory

– Strict control of variables, easy to replicate

– Artificial environment, participants may react differently than real

life (ecological validity?)

• Field

– Natural environment (ecological validity) but can’t control all

variables

• Natural

– Researchers have no control over variables.

– Naturally occurring, researchers are there to study

Confounding Variablesare undesirable variables that influence the relationship

between the IV and DV

• Demand characteristics – Hawthorne affect. Participants act

differently simply because they know they are in an experiment

use single blind control)

• Researcher bias – researcher sees what he is looking for

use double blind control)

• Participant variability use random samples

• Artificiality – ecological validity

Correlational studies

are used to look for relationships between variables.

There are three possible results of a correlational study:

1. a positive correlation,

2. a negative correlation, and

3. no correlation.

• The correlation coefficient is a measure of correlation strength

and can range from –1.00 to +1.00.

• There is no CAUSE-and-EFFECT relationship.