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Research Methods
Chapter 2
Reasoning Fallacies
• Hindsight bias – tendency to believe, after
learning an outcome, that we would have
foreseen it
• The “I knew it all along” phenomenon
Psychology as Science
• Empiricism – belief
that accurate
knowledge of the
world requires
observation of it
• Limitations of casual
observation:
• Unstable
• Can’t tell us about
the properties we
might be interested
in
Psychology as a Science -cont•So we must use measurement to:
• Define the property we want to
measure in concrete terms
• Operational definition – description
of procedures used to define research
variables
• Ex: human intelligence may be
operationally defined as what an
intelligence test measures
Psychology as a Science -cont• A good measurement has
• Validity – allows one to draw accurate
inferences from it
• Replication– produces the same result
whenever it is used to measure the same thing
Case study
• Studying a single individual in depth
Naturalistic observation
• Unobtrusively observing people in their
natural environment
• Avoid demand characteristics – aspects that
cause people to behave as they think an
observer wants/expects them to behave
• Limitations:
• Some things psychologists want to observe
don’t occur naturally
• Some things can only be gathered from direct
observation with a person
Survey
• Survey - uses a representative sample
of people to estimate attitudes or
reported behaviors of a whole
population
• Limitation:
• Respondents may not answer
honestly
Survey -cont• Population - all
the cases in a
group being
studied from
which samples
may be drawn
• Random sample every member of
a population has
an equal chance
of inclusion
Correlational Studies
• Correlation – the
“co-relationship” or
pattern of covariation between
two variables
• Positive – two sets
of variables go up or
down together
• Negative – two sets
of variables relate
inversely
Correlation vs. Causation
• Third-variable
correlation – two
variables may be
correlated only
because they are
both caused by a
third variable
• Correlation does not
prove causation
Correlation -cont• Illusory correlation:
The perception of a
relationship where
none exists
Experimentation
• Used to establish the casual relationship between
variables
• Independent variable – variable that is manipulated
• Is “independent” of what the participant says/does
• Dependent variable – variable that is measured
• “Depends” on what the participant says or does
• Control group – group that does not receive the
treatment
• Experimental group – group does receive the
treatment
Experimentation -cont• An experiment is internally valid when:
• An independent variable has been effectively
manipulated
• A dependent variable has been measured in an
unbiased way with a valid, powerful, and reliable
measure
• A correlation has been observed between the
independent and the dependent variable
• External validity – property of an experiment in
which the IV and DV is operationally defined in a
normal, typical, or realistic way
Experimentation -cont• It is generally not feasible to use a random sample
when conducting an experiment
• Experiments utilize
• Random assignment - assigning participants to
experimental and control groups by chance
• Double blind procedure - neither the research
participants nor the research staff know if participants
received the treatment or a placebo - sugar pill
•
Eliminates placebo effect - experimental results caused by
expectations alone
Measures of Central
Tendency
• Mean – sum of a set of scores in a distribution
divided by the number of scores
• Extreme scores have a greater impact on the
mean than on the mode or median
• Median – score that divides a frequency
distribution exactly in half, so that the same
number of scores lie on each side of it
• Mode – the most frequently occurring score in
a distribution
Measures of Variation
• Definition – a single score that presents
information about the spread of scores in a
distribution
• Range – the highest score in a distribution
minus the lowest score
• Standard deviation – a standard measurement
of how much the scores in a distribution
deviate from the mean
• Normal distribution
• Form a bell-shaped curve
• In a normal distribution of test scores, 50% of
scores fall at or above the mean score and 50%
of scores fall at or below the mean score
• Approximately 1/3 of the scores fall one
standard deviation below the mean and 1/3 fall
one standard deviation above the mean
• All score-based normal
curves have the following
68-95-99.7 rule in
common:
• Approximately 68% of all
scores fall within one
standard deviation of
the mean
• Approximately 95% fall
within two standard
deviations of the mean
• Approximately 99.7% fall
within three standard
deviations of the mean
Skewed distributions
• Positively skewed distributions have more
scores on the low end of the scale
• The median is the best representation of central
tendency
• Negatively skewed distributions have more
scores on the high end of the scale
• The median is a better representative of central
tendency
Ethics
1.
Obtain informed consent – written agreement to
participate in a study made by an adult who has been
informed of all the risks participation may entail
2.
Participation may not be coerced
3.
Psychologists must protect participants from physical or
psychological harm
4.
Risk of embarrassment or minor pain must be outweighed
by social benefits of new knowledge gained by study
5.
Must provide a debriefing – verbal description of true
nature and purpose of study