Single-subject research

Single-subject research is a group of research methods that are used extensively in the experimental analysis of behavior and applied behavior analysis with both human and non-human participants. Four principal methods in this type of research are: changing criterion, reversal ("ABA"), alternating treatments, and multiple baseline. In verbal behavior research the multipleprobe research design is popular.

These methods form the heart of the data collection and analytic code of behavior analysis. Behavior analysis is data driven, inductive, and disinclined to hypothetico-deductive methods. Statistical methods, from The Behavior of Organisms (Skinner 1938) until now, have been largely ignored.

AB research designs
The AB design is the simplest version of this design in which a baseline ("A") is tracked, and then some treatment ("B") is implemented. If there is a change then the treatment is said to have had an effect. However, it is subject to many possible competing hypotheses, making it a very weak research design. The other variants essentially introduce ways to control for the competing hypotheses.

Changing-criterion research designs
In a changing-criterion research design a criterion for reinforcement is changed across the experiment to demonstrate the functional relationship between the reinforcement and the behavior. See Mark Dixon's work with a participant using a short video clip to generate a preference for a progressively delayed variable reinforcement over a fixed shorter delay reinforcement in physical therapy

Reversal or ABA designs
The reversal design is the most powerful of the single-subject research designs showing a strong reversal from baseline ("A") to treatment ("B") and back again. However, many interventions cannot be reversed, some for ethical reasons (e.g., involving self-injurious behavior, smoking) and some for practical reasons (they cannot be unlearned, like a skill)

Alternating-treatment designs
The alternating-treatment design is used in order to ascertain the comparative effect of two treatments. Two treatments are alternated in rapid succession and correlated changes are plotted on a graph to facilitate comparison.

Multiple-baseline designs
The multiple baseline design was first reported in 1960 as used in basic operant research. It was applied in the late 1960s to human experiments in response to practical and ethical issues that arose in withdrawing apparently successful treatments from human subjects. In it two or more (often three) behaviors, people or settings are plotted in a staggered graph where a change is made to one, but not the other two, and then to the second, but not the third behavior, person or setting. Differential changes that occur to each behavior, person or in each setting help to strengthen what is essentially an AB design with its problematic competing hypotheses.

Multipleprobe designs
Popular in Verbal Behavior research, the multiproble research design has elements of the other research designs.