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The Differences in Single Subject Research Design & Group Research Design

Psychologist B.F. Skinner introduced single-subject studies to the field of behavioral reseach with his theory of operant conditioning. Operant conditioning provided stimuli to individuals to observe a freely willed reaction from them. Behavioral research pioneered experimentation with single persons, measuring not only modification of behavior but the intensity or severity of the change.

  1. Control Group

    • By design, the most obvious difference between a single-subject study and multi-participant research is the lack of an outside control group in the single-subject study. A control group represents the status quo and acts as a reference to which the experimental group can be compared. As the name implies, the experimental group can be made of one or more persons who are the objects of observation and/or manipulation. Single-subject study participants act as both their own control and experimental groups.

    Behavioral Research Design

    • According to researcher and author John B. Wasson, when conducting multiple-subject research to observe a hypothesis-dependent variable like a behavioral change, that change is usually only recorded at one time point for each person. Single-subject research design, however, requires that the same dependent variable be observed repeatedly to confirm a definite pattern of behavior or, in this case, a permanent behavior change. Also, only one variable or behavior change can be observed at a time. If two changes occur in single-subject behavioral research, this is considered an interaction. Multiple-subject research can record more than one variable because more participants increases the probability of accuracy and attribution.

    Baseline and Treatment Evaluations

    • Pharmaceutical investigatory research often has a single treatment group under observation for the effects of a specific drug. Before the drug is introduced, baseline data is captured to show a person's physical and/or mental state before starting the drug. This baseline data acts as a reference to which the subject's post-drug evaluations can be compared. This is how all single-subject research must be designed. Multiple-person research offers the option to simultaneously observe a group of people who never receive a drug and a group that does.

    Threat to Study Results' Validity

    • The absence of a separate comparison group in single-subject research design poses a threat to the validity of study results. Broader measures have to be taken to make research findings more definitive. Instead of just taking baseline measures at one time point, internal validity can be bolstered by taking a case history and doing a statistical regression analysis that shows times when a subject is likely to have a dependent variable change. External validity means that the results of a study can be generalized to a greater population. Once again, by design, this is the most difficult claim to make after a single-subject study.

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