Chapter 2
Psychology’s Scientific Method
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Psychology’s Scientific Method
Types of Psychological Research
Research Samples and Settings
Analyzing and Interpreting Data
Conducting Ethical Research
Thinking Critically About Research
The Science of Psychology
How is science different from folk
wisdom?
Where do we find answers to our
questions?
How do you know what to believe?
What separates sense from nonsense?
Critical Thinking
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The Scientific Method
Scientific Method: Observe
Step 1
Observe some phenomenon
curiosity
variables
theory
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Scientific Method: Hypothesize
Step 2
Formulate hypotheses and predictions
testable prediction
derived from theory
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Theories
An explanation for a phenomenon
Should be based on careful and precise
observations
Theories are changeable and expandable,
and most importantly, theories are
FALSIFIABLE.
Theories are falsifiable
In order to be a valid scientific
theory there must be some way that
an observation or experiment could
prove it to be false.
A theory must lead to predictions
that can be tested and either
supported or proven to be false.
Is this theory falsifiable?
The moon is populated by little green men who can
read our minds and will hide whenever anyone on
Earth looks for them, and will flee into deep space
whenever a spacecraft comes near.
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Hypotheses
From theories, psychologists develop
hypotheses.
Hypotheses are predictions about future
behavior.
Specific statement of expectation
derived from theory
State the relationship between two variables
Scientific Method: Research
Step 3
Test through empirical research
operational definition of variables
analyze data using statistical
procedures
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Scientific Method: Conclusions
Step 4
Draw conclusions
replication of results → reliability
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Scientific Method: Evaluate
Step 5
Evaluate the theory
change the theory?
peer review and publication
meta-analysis
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Our hypothesis?
Theory:
Our hypothesis?
Operationalizing the variables
Participants: People? Children? Adults?
Males and/or females?
Independent variable: What kind of
manipulation? Control condition?
Dependent variable: What is our
effect/result? How will we define and
measure that effect?
Research Methods in Psychology
Descriptive
Research
Correlational
Research
The choice of Method
determined by:
Experimental
Research
goal of the research
nature of the problem
being investigated
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Descriptive Research
No manipulation of variables
Weakness?
Can’t infer cause & effect
What you can do:
Can describe patterns of behavior
and discover links or associations
between variables
Descriptive Research
Naturalistic Observation
To study behavior in real-life settings,
Avoid influencing the behavior being
studied (reactive).
Strength – study behavior under natural
conditions
Descriptive Research
Case Study
A case study is an in-depth analysis of a
single person or event.
Allows researcher to gather a lot of info
Although the findings of a case study
may apply only to the person who was
studied, they may provide direction for
further study using other methods.
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Descriptive Research
Survey
Study in which people
are asked questions about
some topic of interest to
the investigator.
By asking questions of a
representative sample,
researchers using the
survey method can
provide useful
information about a
much larger population.
Descriptive Research
Surveys
Use questionnaires or interviews to
gather information
Advantage – can gather data on things
that are difficult to observe
Disadvantages – self-report problems
with intentional deception and wishful
thinking
Descriptive Research:
Pros & Cons
Advantage
Can explore
questions that can
not be examined
with experimental
methods
Disadvantage
Cannot control events to
isolate cause & effect
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Correlational Research
Builds on descriptive designs
Discover how variables change relative to each
other
Cannot tell which variable is causing the
change
Variable X
GPA
Variable Y
SAT scores
Correlational Research
Correlation Coefficient (r)
Ranges from + 1.00 to – 1.00
This number tells you the strength of the
relationship
+/- tells you direction of the relationship
Examples?
Correlational Research
Correlation Coefficient (r)
Variable X
Positive (+) both variables in same direction
Variable Y
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Correlational Research
Correlation Coefficient (r)
Negative (-) values of variables go in
opposite directions
Variable X
Variable Y
Correlational Research
Correlation Coefficient (r)
Correlational Research
Explaining a Correlation
Start with 3 variables, (X, Y, & Z) where X
and Y are correlated:
X may cause Y
Y may cause X
Z may cause X and Y
Correlations indicate relationship patterns,
not causes
They can provide useful insights and help
us to make predictions
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Experimental Research
Experimenter manipulates one variable &
observes changes in another variable
Use of experimental groups to allow
comparison of effects
Because it can generate cause-and-effect
statements, many psychologists believe
that the experimental method is the most
powerful research approach.
Dependent and
Independent Variables
Independent variables -The variables that might
cause an effect
Dependent variable -behavior that shows the
outcome of an
experiment by revealing
the effects of an
independent variable
Experimental and Control Groups
Experimental group -- In some cases participants in an
experiment are exposed to the independent variable
Control group -- Other participants are not exposed to the
independent variable and will be compared with the
experimental group on the dependent variable
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Experimental Research
Experimental Research
By manipulating an independent variable (the
cause), the researcher determines whether it
influences the dependent variable (the effect).
Experimental Research
The only difference between groups should
be the independent variable or variables
manipulated by the experimenter.
If you hold all other extraneous variables
constant, you may identify the cause of the
behavior under consideration.
Want to select 2 groups that are as much alike
as possible before an experiment begins.
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Statistics
Statistics involves the use of mathematics
to organize, summarize, and interpret
numerical data.
Descriptive statistics -- summarize data.
Measures of central tendency
Measures of variability
Coefficient of correlation
Inferential statistics -- used to interpret data
and draw conclusions.
Descriptive Statistics
Measures of Central Tendency
Provide information about the typical score in
a set of numbers.
Median – 50% of scores fall above, 50% below
Mean – arithmetic average
Mode – the most frequent score
Consider these job offers?
COMPANY A:
N=10
Mean=$33,500
Median=$20,000
Mode=$20,000
s.d.=$29,064
Range=$80,000
COMPANY B:
N=10
Mean=$28,000
Median=$22,500
Mode=$20,000
s.d.=$12,293
Range=$35,000
Which job would you choose? Why?
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Measures of Central
Tendency
Income
20,000
Mode = 20,000
20,000
25,000
Median =25,000
35,000
200,000
300,000 / 5 = 60,000
Mean = 60,000
Descriptive Statistics
Measures of Variance
Provide information
about the variability or
spread in a set of data.
Variability – how much
the scores in the data set
vary from each other and
from the mean
Range = high score – low
score
Standard deviation
Inferential Statistics
Used to interpret and draw
conclusions.
Based on laws of probability
Used to evaluate whether the results
of a study may be due to chance
Statistically significant = chances
are less than 5 out of a 100
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Evaluating Research
Flawed research does make its way into
the body of literature.
Replication – can the results of an earlier
study be duplicated
This is why it is important to evaluate
research using:
Critical Thinking
Knowledge of Scientific Method
Knowledge of Research Methods
Evaluating Research
Sampling Bias
Sample is the collection of subjects
selected for observation in an empirical
study
Population is the much larger collection
of people that researchers want to
generalize about.
Sampling bias exists when a sample is
not representative of the population
from which it was drawn.
Evaluating Research
Placebo Effects
Changes in a person's behavior which
come from the EXPECTATION of
change, rather than the ingredients or
components of the treatment they receive.
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Evaluating Research
Distortions in Self-report
Bias introduced by participants who
respond in ways that do not reflect their
actual behavior, beliefs, judgments, etc.
Social desirability bias
Misunderstood or poorly worded questions
“response sets” – participants respond in
automatic ways
Evaluating Research
Experimenter Bias
Bias introduced when a researcher's
expectations or preferences influence
the outcome of the research. This may
be done without the research ever
realizing that he/she is affecting the
outcome.
Double-blind research
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