Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Chapter 2
Scientific Methods in Psychology
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Scientific Methods in Psychology

Science is a word derived from Latin roots: “scientia”
meaning “knowledge.”
 Scientific practice helps psychologists to know that they
have obtained the most accurate and useful knowledge
of mental processes and human behavior.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Module 2.1

Thinking Critically and Evaluating Evidence
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Thinking Critically and Evaluating Evidence
Psychology is a science. This chapter is about how we utilize
scientific methods in evaluating claims and theories in
psychology.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
The Scientific Method

Why do we need it?
 The scientific method provides guidelines for scientists in
all fields, including psychology, to use in evaluating
discrete claims (called hypotheses) and broader
theories.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
The Scientific Method

Why do we need it?
 It is almost impossible to prove with utter certainty that
any individual claim or theory is true beyond a doubt.
 The scientific method allows us to declare our
conclusions to be probable to the point where it is
reasonable to treat them as factual.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Scientific Theories

What is a theory?
 A theory is a comprehensive explanation of observable
events and conditions.
 A good theory makes precise and consistent predictions
while relying on a small number of underlying
assumptions.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Scientific Theories

The importance of falsifiability and parsimony
 A theory that makes precise predictions is falsifiable
because it is easy to think of evidence that would
confirm or contradict the theory.
 Reliance on the fewest and simplest possible
assumptions is called parsimony, and is considered an
essential strength of good scientific theory.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Scientific Theories

Example of a parsimonious and falsifiable scientific theory:
 Gravity is a force that pulls objects in the universe
towards each other.
 According to the theory of gravity, larger and more
massive objects pull smaller objects towards them.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
The Scientific Method
 How do we support claims scientifically?
 Scientists want to know the evidence that will support or
disprove a claim.
 The scientific word for a claim is hypothesis.
 A hypothesis is a testable prediction of what will occur
under a stated set of conditions.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Figure 2.1 A hypothesis leads to predictions. An experimental method tests those
predictions; a confirmation of a prediction supports the hypothesis; a
disconfirmation indicates a need to revise or discard the hypothesis. Conclusions
remain tentative, especially after only one experiment. Most scientists avoid saying
that their results “prove” a conclusion.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
The Scientific Method

What’s the hypothesis?
 Claim: There is a relationship between televised violence
and aggressive behavior.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
The Scientific Method

How do we test the hypothesis? Here are some possible
strategies:
 Measure how much time a sample of children watch
violent television programs and compare that to how
much violent behavior the children exhibit (a
correlational study.)
 Have a group of children watch violent programs and
another group watch non-violent programs, and then
record the differences in amount of violent behavior
between the two groups (an experimental study.)
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
The Scientific Method

How do we measure the results? It is tricky to measure
phenomena such as “violent behavior.”
 We need to operationally define concepts such as
this one; clearly stating which behaviors will represent
the phenomenon of interest (verbal threats, hitting,
etc.).
 And we need to apply the definitions consistently.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
The Scientific Method

What do our results mean?
 If the results support the original prediction, it may mean
the hypothesis is valid, but that does not eliminate other
possible explanations for the outcome.
 If the results contradict the original prediction, the
hypothesis may need to be modified or abandoned
(at least under certain circumstances.)
 Scientists generally do not make any dramatic
alterations to their conclusions based on one study
only.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
The Scientific Method

The importance of replication
 The standards in the scientific community demand that
researchers report their methods in enough detail so that
any other scientist could feasibly repeat the study to
confirm or contradict the validity of the findings.
 Replicable results are those that anyone can obtain, at
least approximately, by following the same procedures.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
The Scientific Method

A good example of an interesting non-replicable result in
psychology is the much-ballyhooed “Mozart effect.”
 Based the results of a single study, researchers claimed
that listening to classical music could improve cognitive
functioning.
 Several other studies have failed to replicate the results
of the original one.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
The Scientific Method

The method of meta-analysis
 Because we sometimes find predominance of small to
medium effects in most studies of a particular
phenomenon (such as sex differences in aggressive
behavior), we may compile the results of a large number
of studies and treat them for all intents and purposes as
one very large research study.
 A meta-analysis also provides us with more information
about the circumstances that will increase or decrease
the likelihood of the predicted effect occurring.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
The Scientific Method

Can you think of examples of evidence that would confirm
or contradict this theory?
EASILY. It is falsifiable.

Does the theory rely on assumptions other than the
existence of the force itself and the effects of size on the
workings of the force?
NO. It is parsimonious.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
The Scientific Method

An example of a claim that is NOT falsifiable:
 The telephone psychic says “Next year, you will go
through a big change.”
 This is not falsifiable because it is too vague.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
The Scientific Method

An example of a claim that is NOT parsimonious:
 The sun goes around the earth. Little gnomes push it
around the sky every day. We can’t see them because
they are invisible to the human eye.
 This is not parsimonious because too many
assumptions must be made in order for the claim to
be accepted as fact.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check

Is this claim falsifiable?
 “You will encounter new challenges in your travels this
week.”
NO
It is vague.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check

“An oversupply of dopamine in the human central nervous
system will eventually result in a decline in the number of
receptors available for that neurotransmitter.”
YES
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check

“On March 19th, 2006, you will meet a 30-year-old
millionaire who will offer you an exciting entry-level job in a
growing high-tech company in Austin, TX.”
YES
Think – why do horoscopes never get this specific?
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check

“Children whose parents divorce will eventually have
serious emotional and relationship problems.”
NOT AS SUCH
The terms “emotional problems” and “relationship problems”
must be operationalized.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check

“There are unseen powers at work in our lives that
scientists will never be able to fully explain.”
NO
This is vague – What powers? How do they work?
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Parsimony and Degrees of Open-mindedness

You might ask  “Shouldn’t we remain open-minded to new possibilities?”
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Scientific open-mindedness:



It is the willingness to consider proper evidence.
It is NOT unquestioning acceptance of any possibility in the
absence of evidence. This is known as “gullibility.”
In other words, your degree of open-mindedness should
have some relationship to the quality of the evidence
presented, including the degree of parsimoniousness of its
interpretation.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
What about anecdotal evidence?



People often use personal accounts of isolated events to
bolster their beliefs in phenomena (such as ESP.)
Because this sort of evidence is not systematically
gathered, it is prone to “selective memory” (called
confirmation bias) on the part of the reporter.
We tend to remember when our hunches come true, and
forget when they do not. We like to be right.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Research on ESP (“Extrasensory Perception”)


Because of the problems described above, anecdotal
evidence is not considered to be acceptable as good
evidence of the existence of ESP.
Experiments done in controlled settings, such as the
Ganzfeld procedure, along with careful observation of some
famous professional psychics, have shown results that
were non-replicable, or easily explainable by techniques of
slight-of-hand known well to experienced magicians.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Psychology as a Science



Science does not deal with proof or certainty.
The history of science is one of constant revision in the face
of new and compelling evidence.
Yet in psychology and all other sciences, we apply the
rigorous and systematic methods of scientific study –
hypothesis, methods, results, and interpretation - to ensure
that our claims are firmly grounded and our revisions reflect
an improved understanding of the phenomena under
scrutiny.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Module 2.2

Conducting Psychological Research
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research


It is essential to your learning in psychology, and perhaps to
your knowledge in general, to be able to evaluate the
quality of the evidence presented in psychological research.
What information do you need to know to be a good
interpreter of psychological research?
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Definitions of Psychological Terms
 The problems of measurement
 We need to measure the phenomena we are
studying.
 Sometimes what we study in psychology is not
tangible. It is not as we are measuring weight or
length of time.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Definitions of Psychological Terms
 The problems of Measurements
 In order to accurately measure these concepts and
phenomena, we develop behavioral or observable
definitions of them.
 We call these definitions operational definitions.
 An operational definition is one that specifies the
operations or procedures used to produce or
measure something. It’s a way to give an intangible
idea a numerical value.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Definitions of Psychological Terms
 So if we are investigating the effect of watching violence
on television on children’s aggressive behavior:
 We need to operationalize “violence” on television.
 We need to operationalize “aggressive behavior.”
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Definitions of Psychological Terms
 Violence might be operationalized as “the number of
times in a one-hour show that one person threatens or
injures another person.”
 Aggressive behavior might be operationalized as “the
number of insults, threats and assaults by the subject
over a 24-hour period after watching a particular
television program”. (There are other versions of both of
these operational definitions that would work well.)
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check

Operational definitions
 Which of the following might be used as an operational
definition of “attraction”?
 A feeling of affection when two people are together. (1)
 The number of minutes during which two people are
touching each other over a four-hour period. (2)

(2)
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check




Which of the following might be used as an operational
definition of “assertiveness?”
The number of times a person makes requests or states his
or her feelings over the course of a one-hour interaction. (1)
An appearance of confidence and ease in social situations.
(2)
(1)
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Population Samples
 Usually in research we are asking questions that are
pertinent to a large population of interest such as:
 Seven to ten-year-old children
 People diagnosed with depression
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Population Samples
 But it is not practical to study all the individuals in the
population.
 We take a relatively small number of observations or
individuals from the population, and we generalize from
that small number.
 The small number of individuals or observations is called
a sample.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Population Samples
 There are several types of samples and sampling
procedures:
 A convenience sample is a group chosen because of
its ease of availability and study.
 A representative sample closely resembles the
population in its percentage of males and females,
ethnic or racial groups, age levels, or whatever other
characteristics might have some relevance to the
results.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Population Samples
 A random sample is one in which every individual in the
population has an equal chance of being selected.
 A cross-cultural sample is one that contains groups of
people from at least two distinct cultures.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Population Samples
 How we go about obtaining a sample has to be carefully
assessed in terms of our resources and goals.
Sometimes it is acceptable and appropriate to rely on a
convenience sample. Other times this strategy will
produce results that are useless in helping us
understand and interpret the “real world.”
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check

Suppose I am interested in the attitudes of college
students towards using the Internet in their studies. I
survey my students in one Introductory Psychology class
at my college.
 Can I assume that their attitudes are representative of
the attitudes of all college students in general?
Not a safe assumption – why?
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Experimenter Bias
 Because (fallible) humans do the research, we need to
keep in check the various tendencies that can work to
create erroneous research findings or erroneous
interpretations of findings.
 Experimenter bias is the tendency of an experimenter to
unintentionally distort the procedures or results of an
experiment based on the expected or desired outcome
of the research.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Experimenter Bias
 For example, if you were a researcher testing the
hypothesis that children who have been diagnosed with
learning disabilities are on average more creative than
children who have no diagnosis, you may find it hard to
“ignore your hypothesis” as you observe the children
with an LD diagnosis going about whatever tasks you
have devised to operationalize “creativity.”
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Experimenter Bias
 Methods have been devised to help counteract these
normal human tendencies that create bias:
 Using blind observers who record data without
knowing what the researcher is studying.
 Using a placebo control. A placebo is a pill or other
sham treatment that makes it very difficult for the
subjects (single-blind) or the subjects and
experimenter (double-blind) to know who has
received the treatment and who has not.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Table 2.2 Single-blind and double-blind Studies
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Figure 2.5 In experiments on sensory deprivation, a person who is deprived of most
sensory stimulation becomes disoriented, loses track of time, and reports
hallucinations. But do these results partly reflect the person’s expectation of having
distorted experiences?
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Research Design
 There are many methods used to study psychological
concepts and phenomena.
 We start by asking ourselves “What happens, and under
what circumstances does it seem to occur?”
 We try to choose the best procedure. Each method has
advantages and disadvantages.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Observational (non-experimental) Research Design
 Naturalistic Observation:
 Careful monitoring and examination of what people
and animals do under more or less natural
circumstances.
 Example: Dr. Jane Goodall’s decades-long
observation of chimpanzees in the forest of
Gombe, recording their social organization and
biological functioning.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Observational Research Design
 Case History:
 A thorough observation and description of a single
individual, appropriate only when done for an unusual
condition or circumstance.
 Example: The case of Phineas Gage, whose
bizarre and unfortunate accident taught medical
doctors and psychologists much about the nature
of the prefrontal cortex of the brain.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Observational Research Design
 Survey:
 A survey is a study of the prevalence of certain
beliefs, attitudes, or behaviors, based on people’s
responses to specific questions.
 Example: Albert Kinsey’s 1948 survey of the
sexual preferences and habits of Americans was
ground breaking, although not by any means
beyond criticism.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Observational Research Design
 Surveys
 A Few Concerns About Survey Research:
 Problems with obtaining a random or
representative sample
 Competence or honesty of those who respond
 The wording of the questions
 Surveyor bias
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Correlational Studies
 Correlation
 Correlation is a measure of the relationship between
two variables which are both outside of the
investigator’s control.
 Examples of variables include aspects such as:
height, weight, socio-economic level, number of years
of education.
 The mathematical estimate of the strength and
direction of a correlation is the correlation coefficient.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Correlational Studies
 The value of the correlation coefficient can range from –
1.00 to +1.00.
 The higher the absolute value, the stronger the
relationship is, regardless of the direction.
 A negative correlation (-) means that as one variable
increases, the other decreases. An example of a
negative correlation is: The more absences a student
has, the lower his or her grade in psychology is (more
absences accompanied by fewer points on tests.)
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Figure 2.8abc In a scatterplot each dot represents data for one person; for example,
each point in the center graph tells us one person’s weight and that person’s grade on
the psychology final exam, in this case using hypothetical data. A positive correlation
indicates that, as one variable increases, the other generally does also. A negative
correlation indicates that, as one variable increases, the other generally decreases.
The closer a correlation coefficient is to +1 or -1, the stronger the relationship.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Figure 2.8a In a scatterplot each dot represents data for one person; for example,
each point in the center graph tells us one person’s weight and that person’s grade on
the psychology final exam, in this case using hypothetical data. A positive correlation
indicates that, as one variable increases, the other generally does also. A negative
correlation indicates that, as one variable increases, the other generally decreases.
The closer a correlation coefficient is to +1 or -1, the stronger the relationship.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Figure 2.8b In a scatterplot each dot represents data for one person; for example,
each point in the center graph tells us one person’s weight and that person’s grade on
the psychology final exam, in this case using hypothetical data. A positive correlation
indicates that, as one variable increases, the other generally does also. A negative
correlation indicates that, as one variable increases, the other generally decreases.
The closer a correlation coefficient is to +1 or -1, the stronger the relationship.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Figure 2.8c In a scatterplot each dot represents data for one person; for example,
each point in the center graph tells us one person’s weight and that person’s grade on
the psychology final exam, in this case using hypothetical data. A positive correlation
indicates that, as one variable increases, the other generally does also. A negative
correlation indicates that, as one variable increases, the other generally decreases.
The closer a correlation coefficient is to +1 or -1, the stronger the relationship.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Correlational Studies
 A positive correlation (+) means that as one variable
increases, so does the other. An example of a positive
correlation would be the higher the annual income, the
greater the amount and number of donations to charity
(more income accompanied by more charitable giving.)
 A zero or near zero correlation means that the variables
have no relationship; that changes in one are not related
to any type of change in the other.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check

What type of correlation?

People’s shoe size and IQ score
Zero
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check

The greater the number of years of education, the higher
the income
Positive
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check

The greater the score on a depression inventory, the lower
the score on a memory test
Negative
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check

Which relationship is stronger?

+. 30 or -.90
-.90
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Correlational Studies
 Some Problems with Interpreting Correlational
Research:
 Illusory Correlation: An apparent relationship based
on casual observations of unrelated or weakly related
events.
 Example: The belief in “moon madness.”
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Correlational Studies
 Some Problems with Interpreting Correlational
Research:
 Correlation  Causation: Correlational research only
tells us if two variables are related and how strongly.
It does not tell us why – two conditions can appear
together and yet not cause each other.
 Example: “The more someone weighs, the larger
his or her vocabulary is.” Do you know why?
Because weight and vocabulary both increase with age.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Figure 2.9 A strong correlation between depression and impaired sleep does not tell us
whether depression interferes with sleep, poor sleep leads to depression, or whether
another problem leads to both depression and sleep problems.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check



Interpreting correlational research
Suppose we did a research study on our campus and found
a -.75 correlation between frequency of exercise and level
of depression.
List all the possible conclusions that we might draw
from this study.

Exercising makes depression less likely.

Depression makes exercising less likely.

A third variable causes increases in exercise and decreases
in depression.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Table 2.3 Comparison of five methods of research
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Experiments
 Experiment:
 A study in which the investigator manipulates at least
one variable (independent) while measuring at least
one other variable (dependent).
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Figure 2.11 An experimenter manipulates the independent variable (in this case the
programs people watch) so that two or more groups experience different treatments.
Then the experimenter measures the dependent variable (in this case pulse rate) to
see how the independent variable affected it.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Experiments
 Example: To test whether the hormone adrenaline
enhances memory in mammals, a researcher teaches
rats to run a maze. She gives a randomly selected
portion of the rats a drug to block production of
adrenaline. She then times all the rats on the maze.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Experiments
 Remember: In order for a study to be a true
EXPERIMENT, one of the variables must be directly
under the researcher’s control, and the other must be
measurable in some scientific way.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Figure 2.12 Once researchers decide on the hypothesis they want to test, they
must design the experiment. These procedures test the effects of watching
televised violence. An appropriate, accurate method of measurement is essential.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check

Is it an experiment? If so, name the independent and
dependent variables.
 A researcher wants to know if men or women are better
at a particular set of spatial relationship tasks. He
compares a randomly selected group of 50 men and 50
women on a test of the task.
Not an experiment – M/F is a subject variable, not a true
independent variable.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check

A researcher wants to know if a particular herbal
supplement is helpful for improving memory. She selects
100 college sophomores who achieved an average score
on a memory test, gives half of them the herb for one
month, half of them an inert pill, and the re-tests them all.
Yes
IV = herb/no herb
DV = score on memory test
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Experiments
 Other important terminology:
 Experimental group: The set of individuals who
receive the treatment that the experiment is designed
to test.
 Control group: The set of individuals who are treated
in the same way as the experimental group except for
the procedure that the experiment is designed to test.
 Random assignment: A selection method in which the
experimenter assigns subjects to either the
experimental or control group using a procedure
based on chance.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Experiments
 Possible problems in carrying out and interpreting the
results of experiments:
 Demand Characteristics: Cues that tell a subject what
is expected of him or her, and what the researcher
hopes to find.
 Example: If the subject knows that the drug being
tested is supposed to improve mood, he or she
may “feel better.”
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Experiments
 Possible problems in carrying out and interpreting the
results of experiments:
 Ethical Considerations: In doing research with
humans or animals, researchers must weigh possible
harm that may be inflicted against the usefulness and
other benefits that may be gained.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Ethical Concerns in Research Involving Human Subjects
 Safeguarding human subjects’ well-being:
 Use of informed consent: Subjects are advised on
what to expect and explicitly state that they agree to
continue.
 Institutional Research Board (IRB) Approval: A
university or other reputable institution appoints a
panel of qualified judges who review all research
proposals before the actual study begins.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Ethical Concerns in Research Involving Human Subjects
 American Psychological Association standards: The
criteria for appropriate treatment of humans who are
experimental subjects are well known to members of this
largest professional organization in the science. Censure
and expulsion are possible consequences for those who
do not follow these procedures.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Ethical Concerns in Research Involving Animals
 Though highly controversial, research studies that use
animals to help us understand the body and brain have
been essential to progress in medicine and psychology.
 Criteria for care and use of animals are established
by professional organizations:
 APA
 The Neuroscience Society
 Animal care committees at research institutions
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
General Principles of Research

Ethical Concerns in Research Involving Animals
 Following the guidelines, animal care committees strive
to:
 Ensure that research animals are treated humanely
 Ensure that any pain and discomfort are kept to a
minimum
 Ensure that all alternatives are examined before
animals are subjected to potentially painful
procedures
 Nonetheless, this area continues to be one of great
debate, and no compromise between the sides ever
seems 100% satisfactory.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Psychological Research
Because of the challenges involved in studying “intangible”
mental processes and human behavior that is the product of
diverse influences, psychologists have developed procedures
that are rigorous and inventive and very frequently do
increase our understanding of the phenomena in this complex
and fascinating science!
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Module 2.3
Measuring and Analyzing Results
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Figure 2.14 Why statistics can be misleading: Both of these graphs present the
same data, an increase from 20 to 22 over 1 year’s time. But by ranging only from 20
to 22 (rather than from 0 to 22), graph (b) makes that increase look much more
dramatic. (After Huff, 1954)
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Descriptive Statistics

Descriptive statistics are mathematical summaries of
results. There are two broad categories of descriptive
statistics:
 Measurements of the Central Score
 Measurements of Variation or Dispersion
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Figure 2.15 Results of an imaginary survey of study habits at one college. This
college apparently has two groups of students—those who study as hard as they
can and those who find other things to do. In this case both the mean and the
median are misleading. This distribution is bimodal; its two modes are 0 and 8.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Descriptive Statistics

Measurements of the Central Score: The Mode
 The mode is the score that occurs most frequently in a
distribution.
 The least useful of the three measures of central score,
it comes in handy when a distribution is very abnormally
distributed (when the majority of scores are clustered at
the low end or high end) or when working with nonnumerical data (categorical variables such as diagnostic
classifications.)
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Descriptive Statistics

Measurements of the Central Score: The Mean
 The mean is the sum of all the scores divided by the
total number of scores. This measure is most useful
when the scores are normally distributed.
 A normal distribution, or normal curve, is a symmetrical
frequency of scores clustered around the mean.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Descriptive Statistics

Measurements of the Central Score: The Median
 The median is the middle score when we arrange all the
scores in order from lowest to highest.
 It is especially useful when the scores we are working
with are very abnormally distributed.
 For example, if our distribution of scores is 2, 3, and 10,
3 is a more accurate description of the “middle” then the
mean, which would be 5 for this set of scores.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Figure 2.16 The monthly salaries of the 25 employees of company X, showing the
mean, median, and mode. (After Huff, 1954)
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check:
Calculate the mean, median and mode for this distribution of
scores:
 2, 3, 4, 4, 7, 10
Mean = 5
Median = 4
Mode = 4
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check


What would be the best measure of central score for this
distribution?
1, 2, 2, 3, 3, 20
Median
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check


What would be the best measure of central score for this
distribution?
4, 4, 4, 4, 4, 4, 7, 8, 10
Mode
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Descriptive Statistics

Measurements of Variation
 The range is a statement of the highest and lowest
scores
 If our distribution has the following scores: 1, 2, 3, 5, 7,
9, 9, 10, the range is from 1 to 10.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Descriptive Statistics

Measurements of Variation
 The standard deviation (SD) is a measurement of the
amount of variation among scores in a normal
distribution.
 The more closely the scores are clustered around the
mean, the smaller the standard deviation is.
 Standard deviations are used to make meaningful
comparisons on different tests or on different versions of
the same kind of test.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Figure 2.17 These two distributions of test scores have the same mean but
different variances and different standard deviations.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check:
On your first statistics exam of the semester, you get a score
of 90, the mean for the class is 70 and the standard deviation
is 20. On the second exam of the semester, you get an 80.
The mean for the class is 65 and the standard deviation is 5.
Did you do better, worse, or the same on the second test?
You did much, much better on exam 2!
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Evaluating Results: Inferential Statistics
As mentioned earlier in the module, we rarely are certain in
the world of research. To infer is to “guess based on
evidence.” Inferential statistics are the mathematical
procedures we use for this educated guessing – a statement
about a large population based on an inference from a small
sample.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Figure 2.18 In a normal distribution of scores, the amount of variation from the mean
can be measured in standard deviations. In this example scores between 400 and 600
are said to be within 1 standard deviation from the mean; scores between 300 and
700 are within 2 standard deviations.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Evaluating Results: Inferential Statistics


Sometimes we try to infer where the “true mean” of the
population of interest is based on the mean of our sample.
 We use a confidence interval to state how sure we are
that the true mean lies within a certain range.
 The calculation of width of the confidence interval is
based on the size of the sample (the larger the better)
and the value of the standard deviation (the smaller the
better.)
Example: “Based on my analysis of this sample, I am 95%
confident that the true population mean lies between 5.0
and 7.0.”
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Evaluating Results: Inferential Statistics

Confidence Intervals
 Confidence intervals are typically reported at the 90%,
95% or 99% levels of certainty.
 The higher the confidence level, the broader the range
that is given by the researcher.
 If the standard deviation is small and the sample on
which the confidence interval is based is large, we can
increase our certainty without necessarily broadening
the range.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
FIGURE 2.19 The vertical lines indicate 95% confidence intervals. The pair of graphs
in part a indicate that the true mean has a 95% chance of falling within a very narrow
range. The graphs in b indicate a wider range and therefore suggest less certainty
that reward is a more effective therapy than punishment.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Evaluating Results: Inferential Statistics

Probability Values
 A probability value is a way to estimate if a score would
be extremely rare given what we know about the likely
range in which the population mean falls.
 If the researcher says that there is a 95% certainty that
the population mean falls between 5.0 and 7.0, and a
particular score falls at 8.2, then that score has a
probability value of less than 5% (p < .05) and it is an
exceptional score in some way.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Evaluating Results: Inferential Statistics

Probability Values and Statistical Significance
 Often scores that are exceptional in this way are
interpreted as being unlikely to have arisen by chance.
 A result that is unlikely to have occurred by chance in a
distribution is interpreted as being statistically reliable or
statistically significant.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Figure 2.21 Researchers say that results are statistically significant if they calculate
that chance variations in data would be unlikely to produce a difference between
groups as large as the one that the researchers actually observed.
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Concept Check:
Which is a more significant result:
 One that is obtained with a p-value of .10 OR
 One obtained with a p-value of .001?
.001
Introduction to Psychology, 7th Edition, James W. Kalat
Chapter 2: Scientific Methods in Psychology
Statistics and Conclusions
Consistent, dependable, large effects do not require statistics
for analysis and interpretation. They speak for themselves.
Psychologists are often dealing with small and fragile effects,
or effects that only arise under a certain set of circumstances.
To do meaningful work in this science, we need a solid
understanding of research design and statistics.