The Science of Psychology
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Copyright © Allyn & Bacon 2006
by Pearson Education.
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What Makes Psychology a
Science?
• Two premises of modern-day science
1. Empiricism
• Acquiring information through careful
observation
2. Theory development
• A psychological theory is a collection of
interrelated ideas and observations that
describe, explain, and predict behavior
and mental processes
Copyright © Allyn & Bacon 2006
What Makes Psychology a
Science?
A. Three scientific principles
1. Objectivity
• Evaluating research and theory on their
own merits
2. Systematic Observation
• Having a plan for gathering data
3. Replication
• Confirming findings through repeated
observations
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What Makes Psychology a
Science?
B. Scientific Method in Psychology
1.State the problem
2.Develop a hypothesis
• An educated guess
3.Design a Study
• Identify variables and responses to examine
• Decide how to define and measure the
variables of interest
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Scientific Method in Psychology
1. State the problem
2. Develop a hypothesis
3. Design a Study
4. Collect and Analyze Data
5. Draw Conclusions and Report Results
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What Research Methods do
Psychologists Use?
A. The Experimental Method
– Systematically manipulating variables and
observing the effects
• Can establish a cause and effect
relationship
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The Experimental Method
• Two types of variables
1. Independent variable (IV)
• Intentionally manipulated by the
experimenter
2. Dependent variable (DV)
• Behavior or response that is expected to
change because of the IV – this is the
factor that is being observed and studied
• Outcome that depends on the IV
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The Experimental Method
• Operational Definition
– How will the variable be measured?
• Participants in the study must be alike on all
variables except the IV
• Participants are randomly assigned to groups
– Experimental group receives the treatment
– Control group does not receive the treatment
• Also known as the comparison group
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The Experimental Method
• If the groups are comparable, you can
conclude that the manipulation of the
independent variable caused changes in the
dependent variable
• If the groups are not comparable, extraneous
variables may “confound the results”
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What Research Methods Do
Psychologists Use?
B. Descriptive Methods
– Describe relationships and events
– Do not manipulate variables
– Therefore, can NOT make inferences about
cause and effect
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Descriptive Methods: 5 Types
1. Case studies
– Intensive study of one case
2. Naturalistic Observation
– Observation of behavior in a naturally
occurring situation
3. Surveys
– Interviews and questionnaires
– Sample must be representative of the
population
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Descriptive Methods
4. Correlational Studies
– Looks for relationships between two
variables
– Because the variables are not controlled,
you can NOT infer causation from
correlational studies
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Descriptive Methods
5. Ex Post Facto Studies
–
Describe differences between groups of
participants that differ naturally on a
variable such as ethnicity or gender
• Variable is NOT manipulated, so these
are not experiments
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How Do Psychologists Evaluate
Research Findings?
Using statistics
– Statistics is a branch of mathematics that
deals with classifying and analyzing data
– Psychologists use two types:
–Descriptive and Inferential
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Using Statistics
1. Descriptive Statistics
a.Measures of Central Tendency
i. Mean
 Average
ii. Median
 Middle Score
iii. Mode
 Most common score
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Descriptive Statistics
Measures of Variability
Range
• Highest minus lowest score
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STANDARD DEVIATION
A measure of the variability of the scores.
How closely do the scores cluster around the
mean?
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Descriptive Statistics
Correlation Coefficients
– Numerical way to describe the relationship
between two variables
– Ranges from –1 to +1
– Positive correlation coefficients indicate
that
•
•
As one variable increases, the other
increases
As one variable decreases, the other
decreases
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Correlation Coefficients
•
Negative correlation coefficients indicate that
– As one variable increases, the other
decreases
• Closer to |1| (-1 or +1), the stronger the
relationship
• Closer to 0, the weaker the relationship
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Using Statistics
2. Inferential Statistics
– Used to determine if research results are
significant
– Significant differences are statistically
unlikely to occur because of chance alone
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How Do Psychologists Evaluate
Research Findings?
Avoiding Bias in the Research Process
– Several different types of bias:
1. Ethnocentrism
– A tendency to believe one’s group is the
standard against which other groups
should be judged
– Implies the superiority of one’s own group
– Leads to distortion and prejudice
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Avoiding Bias
2.
Race, ethnicity, culture, and social class
– Ethnicity is a more valuable construct than
race
– Behavior must be viewed as occurring in a
cultural context
– Cultures can be individualist or collectivist
• Individualist cultures stress personal goals
and value individual freedom
• Collectivist cultures stress group needs
– Social class (education, income, and
occupational status or prestige) also affects
behavior
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Avoiding Bias
3. Gender
– Women and men may react differently in the
same situation
4. Sexual orientation
– Differs from sexual behavior
– Three sexual orientations are recognized
– Homosexual
– Heterosexual
– Bisexual
– Unrelated to psychological maladjustment
– Homophobia
– Heterosexism
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Avoiding Bias
5. Age
– Older people are a growing percentage of the
population
6. Disability
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Avoiding Bias
7. Diversity Within and Between Groups
– There are usually more differences within a
group than between groups
– Generalizations are virtually impossible
– Therefore, psychologists emphasize individuals
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Ethical Principles
• Rules concerning proper conduct in research
• Human participants:
– Must give informed consent
– Cannot be coerced
– Can decline to participate at any time
• Information is kept confidential
• Debriefing: A post-experimental interview that
explains the study
• Deception can only be used if it has overriding
scientific, educational, or practical value
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Point – Counterpoint
Should Nonhuman Animals Be Used in
Research?
No
• Animals are subjected to painful treatments under the
assumption they are “lesser” than humans
• Information may not be generalizable to humans
Yes
• Research with animals has allowed for important
studies that would be impossible with humans
• The information from such studies is directly relevant
for improving people’s lives
What do you think?
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