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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.
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