Transcript Comer, Abnormal Psychology, 5th edition

Chapter 2
Research in Abnormal Psychology
Research in Abnormal Psychology
 Clinical researchers face certain challenges that
make their investigations particularly difficult:
• Measuring unconscious motives
• Assessing private thoughts
• Monitoring mood changes
 Clinical researchers must consider the cultural
backgrounds, races, and genders of those they study
 Clinical researchers must follow the code of ethics
to ensure that their subjects are not harmed
Slide 2
What Do Clinical Researchers Do?
 Clinical researchers try to discover laws and
principles of abnormal psychological functioning:
• Generally do not assess, diagnose, or treat individual
clients
• Search for nomothetic understanding
• General or universal laws
• Use the scientific method to pinpoint relationships among
variables
• Use three methods of investigation…
Slide 3
The Case Study
 Provides a detailed description of a person’s life &
psychological problems
 Is helpful because it can serve as a source of new
ideas about behavior
• Freud’s theories based entirely on case studies
 May offer tentative support for a theory
 May challenge a theory’s assumptions
 May inspire new therapeutic techniques
 May offer opportunities to study unusual problems
Slide 4
The Case Study
 Has limitations:
• Observers are biased
• Relies on subjective evidence
• Is low on internal validity
• Provides little basis for generalization
• Is low on external validity
 These limitations are addressed by the two other
methods of investigation…
Slide 5
The Correlational Method &
the Experimental Method
 Do not offer richness of detail
 Allow researchers to draw broad conclusions
• Typically involve observing many individuals
• Researchers apply procedures uniformly
• Studies can be replicated
• Researchers use statistical tests to analyze results
Slide 6
The Correlational Method
 Correlation is the degree to which events or
characteristics vary from each other
• Measures the strength of a relationship
• Does not imply cause and effect
 The people chosen for a study are its subjects
or participants, collectively called a sample
• The sample must be representative
Slide 7
The Correlational Method
 Correlational data can be graphed and a “line
of best fit” can be drawn
• Positive correlation = variables change in the
same direction
Slide 8
Positive Correlation
Slide 9
The Correlational Method
 Correlational data can be graphed and a “line
of best fit” can be drawn
• Negative correlation = variables change in the
opposite direction
Slide 10
Negative Correlation
Slide 11
The Correlational Method
 Correlational data can be graphed and a “line
of best fit” can be drawn
• Unrelated = no consistent relationship
Slide 12
No Correlation
Slide 13
The Correlational Method
 The magnitude (strength) of a correlation is
also important
• High magnitude = variables which vary closely
together; fall close to the line of best fit
• Low magnitude = variables which do not vary as
closely together; loosely scattered around the line
of best fit
Slide 14
High (Positive) Correlation
Slide 15
Moderate (Positive) Correlation
Slide 16
The Correlational Method
 Direction and magnitude of a correlation are often
calculated statistically
• Called the “correlation coefficient,” symbolized by the
letter “r”
• Sign (+ or -) indicates direction
• Number (from 0.00 to 1.00) indicates magnitude
• 0.00 = no consistent relationship
• +1.00 = perfect positive correlation
• -1.00 = perfect negative correlation
 Most correlations found in psychological research
fall far short of “perfect”
Slide 17
The Correlational Method
 Correlations can be trusted based on statistical
probability
• “Statistical significance” means that the finding is
unlikely to have occurred by chance
• By convention, if there is less than a 5% probability
that findings are due to chance (p < 0.05), results are
considered “significant” and thought to reflect the
larger population
• Generally, confidence increases with the size of
the sample and the magnitude of the correlation
Slide 18
The Correlational Method
 Advantages of correlational studies:
• Have high external validity
• Can generalize findings
• Can repeat (replicate) studies on other samples
 Difficulties with correlational studies:
• Lack internal validity
• Results describe but do not explain a relationship
Slide 19
Slide 20
The Correlational Method
 Two special forms of correlational study:
• Epidemiological studies
• Reveal the incidence and prevalence of a disorder in a
particular population
• Incidence = number of new cases in a given time period
• Prevalence = total number of cases in a given time period
• Longitudinal studies
• Observe one sample of participants on many occasions
over a long period of time
Slide 21
The Experimental Method
 An experiment is a research procedure in which a
variable is manipulated and the manipulation’s
effect on another variable is observed
• Manipulated variable = independent variable
• Variable being observed = dependent variable
 Allows researchers to ask such questions as: Does
therapy X reduce symptoms of disorder Y?
• Causal relationships can only be determined through
experiments
Slide 22
The Experimental Method
 Statistics and research design are very important
• Researchers must eliminate all confounds – those
variables other than the independent variable that may
also be affecting the dependent variable
• Three features are included in experiments to guard
against confounds:
• The control group
• Random assignment
• Blind design
Slide 23
The Experimental Method
 A control group is a group of participants who
are not exposed to the independent variable,
but whose experience is similar to that of the
experimental group
• By comparing the groups, researchers can better
determine the effect of the independent variable
 Rules of statistical significance are applied
Slide 24
The Experimental Method
 Researchers must also watch out for
preexisting differences between the
experimental and control groups
• To do so, researchers use random assignment –
any one of a number of selection procedures that
ensures that every participant in the experiment is
as likely to be placed in one group as another
• Examples: coin flip; drawing names from a hat
Slide 25
The Experimental Method
 A final problem with confounds is bias
• To avoid bias by the participant, experimenters employ a
“blind design,” in which participants are kept from
knowing what condition of the study (experimental or
control) they are in
• One strategy for this is providing a placebo – something that
looks or tastes like real therapy but has no key ingredient
• To avoid bias by the experimenter, experimenters employ
a “double-blind design,” in which both experimenters and
participants are kept from knowing what condition of the
study participants are in
• Often used in medication trials
Slide 26
Alternative Experimental Designs
 In natural experiments, nature manipulates the
independent variable and the experimenter
observes the effects
• Example: psychological impact of flooding
• Cannot be replicated at will
• Broad generalizations cannot be made
Slide 27
Alternative Experimental Designs
 Analogue experiments allow investigators to freely
manipulate independent variables while avoiding
ethical and practical limitations
• They induce laboratory subjects to behave in ways that
seem to resemble real life
• Example: animal subjects
• Major limitation of all analogue research is that
experimenters cannot be certain that the phenomena
observed in the lab are the same as the psychological
disorders being investigated
Slide 28
Alternative Experimental Designs
 In a single-subject (“n of 1”) experiment, a
single participant is observed both before and
after manipulation of an independent variable
• Experiments rely on baseline data to set a
standard for comparison
• Common experimental designs are ABAB and
multiple-baseline designs
Slide 29
Alternative Experimental Designs
 In ABAB (reversal) designs, a participant’s
reactions are measured during a baseline
period (A), after the introduction of the
independent variable (B), after the removal of
the independent variable (A), and after
reintroduction of the independent variable (B)
• The subject is, essentially, compared against him
or herself rather than against control subjects
Slide 30
Alternative Experimental Designs
 Multiple-baseline designs examine two or
more dependent variables for change when an
independent variable is introduced
Slide 31