Single-Case Designs and Small n Research
Overview of Psych Methods
Survey Methods
Single-Case Designs and Small n Research
Repeated Measures Designs
Introduction to Complex Designs
Experiments vs Non-Experiments
Threats to Internal Validity
Scientific Method
Complex Design
Review Questions
Cafe Scientifique

Single-Case Research

n    Single-case research is idiographic rather than nomothetic.

n    These designs are often used in clinical psychology and neuropsychology.

n    The two major types of single-case research designs are:

n  case study, and

n  single-subject experimental designs

Case Study Method

n    Case study: An intensive description and analysis of a single individual.

n   Data: clinical observations, self-report, archival data (e.g., medical records)

n   Case studies typically report the results of a treatment.

n   Major problem: Lack scientific control

n simultaneous treatments, extraneous variables


Advantages of the Case Study Method

n   rich source of ideas for developing hypotheses,

n   opportunity for clinical innovation,

n   method for studying rare events,

n   possible challenge to theoretical assumptions,

n   tentative support for a psychological theory, and

n   complement to the nomothetic study of behavior


Disadvantages of the Case Study Method

n   difficulty drawing cause-and-effect conclusions (limited internal validity),

n   possible biases when interpreting outcomes due to observer bias and biases in data collection (e.g., due to poor memory), and

n   problem of generalizing findings from a single individual (limited external validity)


Case Study Method (continued)

n    Case studies provide great anecdotal evidence and “testimonials.”

n    Case studies that appear in the popular press are rarely scientific.

n    People want to believe that the treatment in these testimonials will work for them, but often they do not.

n    It’s better to pay attention to the results of single-subject experiments.


Single-Subject Experimental Designs

n    Single-subject experimental designs have their roots in B. F. Skinner’s approach called applied behavioral analysis.

n    Single-subject designs improve on case studies, because the researcher attempts to gain more scientific control.


Characteristics of Single-Subject Experiments

n    Critical feature of single-subject designs: An independent variable is examined:

n   treatment

n   no treatment control (baseline stage)

n    Researchers compare treatment conditions for one individual whose behavior is continuously monitored (repeated measures).


         The baseline condition is used to describe behavior before treatment is provided, and predict what behavior will be like in the future without treatment.

         Compared to baseline, the behavior decreases after treatment is implemented.

         Although this pattern of data suggests the treatment was effective, some other factor that occurred at the same time as the treatment could have caused the frequency of behavior to decrease.


         The ABAB Design: Baseline and Treatment conditions are contrasted in the ABAB Design

         Illustration of a Treatment Effect: The frequency of the behavior decreases during treatment (B),  reverses when treatment is withdrawn (second A), and reverses again during treatment (second B).


ABAB Design

Illustration of no reversal:

When the frequency of behavior does not reverse when treatment is withdrawn (second A), it is very difficult to determine whether the treatment was effective. Why?


n    Methodological Issues Associated with ABAB Designs

n    If behavior does not reverse back to baseline levels after treatment is withdrawn, researchers cannot conclude that treatment caused the initial behavior change.

n    A variable other than treatment may have caused the behavior to change.

n    Treatment may have promoted change, and then other variables (e.g., positive attention) may persist to maintain behavior change.

n    Some behaviors may not be logically expected to change once improved (e.g., when new skills are learned).


n    Ethical considerations

n   Is it ethical to remove a treatment that appears to be beneficial (i.e., implement the second “A” baseline stage)?

n   Dilemma between goal of understanding and goal of creating change.


Multiple-Baselines Design

n    The multiple-baselines design solves this ethical problem.

n   establish several baselines

n   implement treatment in one baseline at a time

n   compare behavior in treatment and baseline stages

n    Multiple baselines can be implemented

n   across situations

n   across behaviors

n   across individuals

n    Interpretation:

n   If treatment is effective, behavior changes when the treatment is implemented and does not change for the remaining baselines.

n   Behavior changes only when the treatment is implemented and directly following the introduction of treatment.

Multiple-Baselines Design (continued)

n    How many baselines are needed?

n   A minimum of two; three or four are recommended.

n    What if behavior changes before the intervention?

n   The reasons for behavior change become hard to interpret; researchers analyze the situation to see if some aspect of treatment generalized.

n    What if the treatment generalizes to other behaviors, situations, or individuals?

n   Researchers should try to anticipate when generalization may occur and modify their research design accordingly.


Problems with All Single-Subject Designs

n    Baseline Records

n   If baselines demonstrate unstable, increasing, or decreasing trends in behavior, the effects of treatment are hard to interpret.

n   When baseline behavior shows extreme variability, it’s difficult to detect a clear discontinuity in behavior when treatment is implemented.

n   Solutions: Look for factors that may contribute to variability, wait for baseline behavior to stabilize, average baseline data points across observations.

n   Whether increasing or decreasing baseline trends are a problem depends on the desired direction of behavior change.

n   Suppose the goal is to increase the frequency of a behavior.

n  If the baseline shows an increasing frequency of behavior, determining whether behavior increases following treatment will be difficult.

n  However, if the baseline shows a decreasing trend and treatment reverses this trend, we can be confident about the effect of the treatment.


n    External Validity

n   Single-subject designs are frequently criticized for their limited external validity.

n   Will treatment effects observed for one individual generalize to other individuals?

n   Reasons why external validity may not be limited:

n Treatments are usually powerful.

n Multiple-baselines designs can be used to demonstrate generality of effects.

n Group treatment can be used to demonstrate effectiveness of treatment.

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