Single-Subject Designs

doi:10.1097/00004583-200010000-00023

Journal of the American Academy of Child & Adolescent Psychiatry

Volume 39, Issue 10, October 2000, Pages 1327-1329

https://doi.org/10.1097/00004583-200010000-00023 Get rights and content

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Reversal Designs

In these designs (Fig. 1), the first A stands for the baseline period, during which the participant is usually observed for a number of time periods. In single-subject designs, the investigator plots the data for each measurement period on graph paper to determine whether the behavior during baseline (or treatment) is increasing, decreasing, or leveling off. The first B period refers to the first intervention period. After the baseline has leveled off, the investigator initiates the treatment

Multiple-Baseline Designs

Multiple-baseline single-subject designs were introduced more recently. Multiple baseline designs were introduced because (1) in clinical situations the removal of treatment is often considered unethical, especially if the treatment appears successful; and (2) many of these studies were being performed in settings in which the patient was responsible for payment for the treatment. In multiple-baseline studies, in the initial stages of the study as many as 3 baselines may be recorded

Measurement Periods and Instruments

In a reversal design, the number of measurement periods may change between one phase and another. One should wait until each phase is stable before starting or withdrawing treatment. This adds to the flexibility of the design. On the other hand, within each measurement period (session), the length of time must be the same.

A second measurement issue to consider when performing single-subject designs is that the type of instrument selected could seriously compromise the study. Each session must

Evaluation of the Results of Single-Subject Designs

Many early single-subject studies with animals did not use statistical analysis. Instead, the investigators believed that the graphic displays were convincing. However, single-subject studies with humans, especially reversal designs, usually have fewer baseline and intervention periods than animal studies. In addition, single-subject designs often have a problem of serial dependency (responses within the same individual are correlated, and thus future responses are partially predictable).

Considerations of Internal and External Validity of Single-Subject Designs

Internal validity problems relate to problems in random assignment. With only one participant, there cannot be random assignment of participants to treatments. More important, the order of the treatment phases also cannot be randomly assigned. A third problem is possible carryover effects from one phase to another. On the other hand, the ABAB design reduces the threats of confounding.

The problems in external validity for single-subject designs are even more obvious. The random selection of one

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REFERENCES (3)

A Kazdin
Single-Case Research Designs
(1982)

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: The authors thank Helena Chmura Kraemer for a helpful critique and Nancy Plummer for manuscript preparation. Parts of the column are adapted, with permission from the publisher and the authors, from Gliner JA and Morgan GA (2000), Research Methods in Applied Settings: An Integrated Approach to Design and Analysis. Mahwah, NJ: Erlbaum. Permission to reprint or adapt any part of this column must be obtained from Erlbaum.

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