BA200 Unit 3 Single-Subject Design Case Analysis Example

Four Phases and a Break Card: A BA200 Unit 3 Single-Subject Design Case Analysis of Biting

[Student Name]

Purdue University Global

BA200: Conceptual Foundations of Applied Behavior Analysis

Unit 3 Single-Subject Design Case Analysis

[Instructor Name]

[Date]

The child, the clinic, the team and every data point are composite and illustrative; the studies and texts cited are real.

The Case

Mateo is a five-year-old autistic boy who comes to the western Colorado clinic where I work. In the fall he began biting peers during the clinic's morning circle time, a twenty-minute group activity with songs and turn-taking. Bites broke the skin twice and upset other families. My supervising behavior analyst designed an assessment and intervention, and I collected most of the data during sessions. This paper analyzes the single-subject design she used.

Why Single-Subject Research

Applied behavior analysis relies heavily on single-subject designs, in which one person's behavior is measured repeatedly under different conditions, and the person serves as his own control. Baer et al. (1968) named analytic as one of the defining dimensions of applied behavior analysis: an intervention is analyzed when the researcher can show believable control over the behavior, so that changes in behavior follow changes in the intervention. Kazdin (2011) describes the logic of these designs as resting on repeated measurement, a stable baseline and a pattern of change that would be unlikely if the intervention had no effect.

Assessment

Before any intervention, the team needed to know why Mateo was biting. A brief functional analysis, following the approach introduced by Iwata et al. (1994), tested whether biting was maintained by attention, escape from demands, access to items or automatic reinforcement. Bites occurred almost only in the demand condition, in which the therapist asked Mateo to complete tasks and briefly removed the demand when he bit. Combined with circle time data showing that bites usually ended his participation, the results pointed to escape: biting got Mateo out of a demanding group activity.

The Intervention

Carr and Durand (1985) showed that problem behavior maintained by escape or attention could be reduced by teaching children a communicative response that produced the same consequence, an approach called functional communication training. For Mateo, the team taught him to hand a staff member a break card, which earned a two-minute break on a beanbag at the side of the room. Bites no longer produced escape; staff kept him in the circle with physical safety precautions while prompting the card.

The break card did not ask Mateo to stop wanting a break; it gave him a safer way to get one.

The Design and the Data

The team used an ABAB reversal design across twenty-six circle time sessions. In the first baseline phase, five sessions, bites averaged about six per session, ranging from four to eight, with no clear trend. In the first intervention phase, eight sessions, bites fell steadily to about one per session by the end, and Mateo used the break card two to four times a session. In a brief return to baseline, four sessions in which the card was unavailable, bites rose to an average of about five. When the card was reintroduced for nine sessions, bites fell quickly to fewer than one per session and stayed there.

Visual analysis of the graph supports the conclusion that the intervention, not some other change, reduced biting. The level of behavior changed each time the condition changed, in the predicted direction, and the change was replicated. A coincidental event, such as a new classroom aide or a change in Mateo's sleep, would be unlikely to produce a drop, a rise and a second drop timed to the phase changes.

What Came Next

A break card that works can create its own problem. In the final phase, Mateo asked for a break as often as every three minutes on some days, which kept him safe but out of much of circle time. The team then began thinning the schedule: first by asking him to complete one short activity before the card was honored, then two, and by adding a visual timer that showed when the next break would be available. Over the following month, his requests fell to about two per session while bites stayed near zero.

The team also checked whether the skill would generalize. During snack time, where Mateo had never bitten but sometimes pushed away his tray, staff placed a break card on the table without teaching it there. He used it on the second day. That observation was informal, not part of the design, but it suggested the communication skill was not tied to one room.

Strengths and Limitations

The design's main strength is its demonstration of experimental control within one child, which is exactly what a clinician needs before recommending the intervention for that child. Data were collected every session, using a simple tally of bites per circle time, and a second observer recorded bites in about a third of sessions, with high agreement, which supports reliability.

The design also has limits. Its findings apply to Mateo; whether functional communication training would work for another child requires replication, though the published literature provides much of that. Phase lengths were short, especially the reversal, so the data cannot show long-term maintenance. Generalization to settings other than circle time was not tested.

Was a Reversal Appropriate?

The most serious question is ethical. Biting hurts other children, and the reversal phase deliberately removed an intervention that was working, which predictably increased bites. The team limited the reversal to four sessions, added staffing and seating changes to protect peers during that phase, and discussed the plan with Mateo's parents, who agreed.

A multiple baseline design, introducing the intervention at different times across settings such as circle time, snack and outdoor play, could have shown control without removing the intervention. My supervisor chose the reversal because circle time was the only setting with frequent biting, which made a multiple baseline across settings impractical. In my view, the choice was defensible given the safeguards, but a reader should weigh the cost of the reversal against the strength of the evidence it produced.

Conclusion

Mateo's case shows how a single-subject reversal design can demonstrate that an intervention, in this case a break card replacing biting, controls behavior for one child. The data meet the logic of the design: repeated measurement, stable baselines and replicated change. The case also shows the ethical cost of that logic when the behavior harms others, and why the choice of design is a clinical decision as well as a scientific one.

References

Baer, D. M., Wolf, M. M., & Risley, T. R. (1968). Some current dimensions of applied behavior analysis. Journal of Applied Behavior Analysis, 1(1), 91-97. https://doi.org/10.1901/jaba.1968.1-91

Carr, E. G., & Durand, V. M. (1985). Reducing behavior problems through functional communication training. Journal of Applied Behavior Analysis, 18(2), 111-126. https://doi.org/10.1901/jaba.1985.18-111

Iwata, B. A., Dorsey, M. F., Slifer, K. J., Bauman, K. E., & Richman, G. S. (1994). Toward a functional analysis of self-injury. Journal of Applied Behavior Analysis, 27(2), 197-209. https://doi.org/10.1901/jaba.1994.27-197

Kazdin, A. E. (2011). Single-case research designs: Methods for clinical and applied settings (2nd ed.). Oxford University Press.