Psychological Science
The Need for Psychological Science
The Limits of Intuition
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Hindsight Bias
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Overconfidence
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We tend to think we know more than we do
Heuristics
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We tend to believe, after learning an outcome, that we
would have foreseen it
the “I-knew-it-all-along” phenomenon
A “rule of thumb” problem solving technique
Confirmation Bias
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Our tendency to seek out information that confirms our
previous beliefs and to ignore information that refutes
them.
The Scientific Attitude
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Critical Thinking
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thinking that does not blindly accept
arguments and conclusions
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examines assumptions
discerns hidden values
evaluates evidence
How do we know what we know?
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How do you know that George Washington was
the first President of the United States?
How do you know that you really have a
stomach?
What makes you sure the sun will rise
tomorrow?
How do you know the color of the shirt you are
wearing?
How can you be sure there aren’t little creatures
inside a computer that make it work?
How do we know what we know?
Authority – we take the word of an expert
 Reason – deductive an inductive thinking
to arrive at a conclusion
 Observation – your own experience
 All three ways of knowing are used by
scientists, but observation must be the
basis for knowledge that is scientific
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The Scientific Method
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Theory
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an explanation using an integrated set of
principles that organizes and predicts
observations
Usually a statement about relationship
between two variables
Hypothesis
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a testable prediction
 often implied by a theory
The Scientific Method
The Scientific Method
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Replication
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repeating the essence of a research
study to see whether the basic
finding generalizes to other
participants and circumstances
usually with different participants in
different situations
Replication is made possible by
Operational Definitions
The Scientific Method
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Operational Definition
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a statement of procedures (operations)
used to define research variables
Example
intelligence may be operationally defined as
what an intelligence test measures
Flaws in Surveys
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What are some of
the flaws that you
can think of with
surveys?
 Wording
 Audience
 Order
 Who
is asking?
Flaws in Surveys

Wording:
 How
can the wording of a
survey influence the
responses given?
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“Sex” vs. “Relations”
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“Hate” vs. “Dislike”
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“Love” vs. “Like”
Flaws in Surveys
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Audience:
 How can the
audience to which
the survey is given
influence the
responses?
Location and topic
 How are the
questions asked?
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Order:
 How
Flaws in Surveys
can the order
in which the
questions are
asked influence
the responses?
-1.) Do you think the actions of the
Sept. 11th attacks were wrong?
-2.) Does it anger you that
American soldiers are dying in
Iraq?
-3.) Do you think people in the
Middle East are generally violent?
Random Samples
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Why is it important to have random samples in
survey research?
 Some
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fun statistics:
68% of people roll toilet paper over the spool
79% squeeze toothpaste from the top
7% look behind the shower curtain when using someone
else’s bathroom
80% of people eat corn on the cob in circles instead of rows
10% of people have seen a ghost
7% of people have flossed their teeth with their own hair
Random Samples
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What was wrong
with each one of
those statistics?
 Those
responses
were the results of
only about 7,000
people out of 25,000
surveyed.
Random Samples
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Acquiring random
samples is not as easy as
it looks, but is very
important to at least
“attempt” to do with any
survey.
 American
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Idol (ughhh)
How are their “phone or text
in” surveys not as random as
they seem?
You better feel strong enough
about your vote to want to pay
$1.00 or whatever it is.
Random Samples
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Obtaining random samples for any purpose is
difficult. The government has had no more
success than the private sector.
 The
1970 lottery to determine the order of the military
draft was almost certainly unfair.
 The 31 capsules for January were placed in the bin
first, then the 29 for February, and so on until the 31
for the next December.
 What do you think happened when the bin was not
turned enough?
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The December Birthdays were drawn much earlier.
Correlation and Cause/Effect
Misinterpretations
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What is Correlation? Seriously, who here
knows?
RELATIONSHIP….Not cause!
Correlation should not be interpreted as a
cause and effect.
It is very easy to misinterpret correlation
studies as a cause an effect issue, but this is
not accurate.
Pellagra example.
Correlation and Cause/Effect
Misinterpretations
A Story;
In the early twentieth century,
thousands of Americans in
the South died from Pellagra,
a disease marked by
dizziness, lethargy, running
sores, and vomiting.
Correlation and Cause/Effect
Misinterpretations
Finding that families struck with the
disease often had poor plumbing and
sewage, many physicians concluded
that pellagra was transmitted by poor
sanitary conditions.
In contrast, Surgeon General Joseph
Goldberger thought that the illness was
caused by an inadequate diet.
Correlation and Cause/Effect
Misinterpretations
He felt that the correlation between
sewage conditions and pellagra did not
reflect a casual relationship, but that the
correlation arose because the
economically disadvantaged were likely
to have poor diets, as well as poor
plumbing.
So, how was the controversy resolved?
Correlation and Cause/Effect
Misinterpretations
Well, the answer demonstrates the
importance of the scientific
method.
To prove he was right, Goldberger
not only had himself injected with
the blood of a victim with sores
all over his body, he found a
victim with diarrhea and….ate his
excrement!
He did NOT come down with
pellagra!
Correlation and Cause/Effect
Misinterpretations
To further make his case, Goldberger asked
two groups from a Mississippi state prison
farm to volunteer for an experiment. One
group was given a high carbohydrate, low
protein diet that Goldberger suspected to
be the culprit, while the other received a
balanced diet. Within months, the first
group was ravaged by pellagra, while the
second showed no signs of the disease.