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Single-Subject Design Examples

There are three commonly employed single subject research designs.

  1. A-B-A-B Withdrawal (Reversal) Designs
  2. Multiple-Baseline Designs
  3. Alternating Treatments Design

A-B-A-B Withdrawal (Reversal) Designs

The A-B-A-B withdrawal procedure uses a baseline (control) phase referred to as the A of the experiment and an intervention (treatment) phase of the experiment known as the B. In the A-B-A design, the baseline is required to establish the student’s pre-intervention performance level. This non-intervention period is initiated until the behavior in question demonstrates stability. The intervention phase B of the study is initiated and data continues to be collected. In the A-B-A design, a third phase is subsequently instituted in which the experimental intervention is withdrawn with a return to the baseline (control) state A. Finally, the B phase is reinstated to demonstrate that the effects are a function of the intervention and not some other variable. This is done to determine if a causal relationship exists between the intervention (B) and improved student performance. Demonstrating the effect across additional participants further strengthens the causal relationship.


Example: A-B-A-B Withdrawal Design
A teacher is working to improve a student’s ability to remain in seat during work periods uses an A-B-A-B Design.

  • Phase A: The teacher records the number of times per day Bob is out of his seat during work periods.
  • Phase B: The teacher implements reinforcement program for student remaining in seat for a week and counts the frequency of out of seat behavior.
  • Phase A: The teacher suspends the reinforcement program and the records the number of times Bob is out of his seat.
  • Phase B: The teacher re-implements reinforcement program for student remaining in seat and counts the frequency of out of seat behavior.

In this experiment the teacher is able to show the reinforcement program is effective in meeting her goals for Bob.

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Multiple-Baseline Designs

The first example looked at the effects of a single targeted student behavior, out of seat, in a single setting.

The second example, a multiple-baseline design, is useful for studying the effects of a teaching practice in which two or more behaviors, people, or settings can be tracked on a single experiment. The multiple-baseline can examine one of these three variables (subject, behavior, or setting) while keeping the other two variables constant. In the A-B-A-B design all three parameters were kept constant, a single behavior for a single subject in a single setting. What if a teacher wants to know the impact of fluency training for three students in her/his classroom? The multiple-baseline design is well suited to answering this type of question. Another advantage of the multiple baseline design is it is not necessary to return a participant to baseline condition.  The multiple baseline design can demonstrate causal relation without having to terminate intervention.  In the case of academic skills this offers the teacher an important tool as it is often the case that once the skill have been learned then a return to baseline will not produce a change in performance.

Example: Multiple-Baseline:

A pre-intervention reading fluency baseline is established for all three students (Bill, Gloria, and Bob). The data is usually collected concurrently across all three participants.

After three to five trials and assuming a stable baseline is established, Bill is introduced to the experimental condition, a reading fluency  program. The program is introduced while the other two subjects continue with the baseline condition.

After three to five more trials, Gloria goes into the experimental phase. The third student, Bob, continues with the baseline condition.

After three to five more days, Bob starts the experimental phase while the other two participants continue in the intervention phase.

In this example, the dependent variable is the number of words read correctly during a one-minute time period, and the independent variable is the three students.
This design allows the teacher to know that the intervention is effective for Bill and Gloria but is not working for Bob.
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Alternating Treatment Design

The alternating treatment design is used to compare the effects of two treatments on one subject. Two interventions or practices are introduced and alternated at each of the training sessions. The teacher determines randomly which of the two experimental interventions to select for each session. This design offers the teacher a method for comparison of the two interventions is better suited to improving the student’s performance.

Example: Alternating Treatment Design

A teacher is interested in increasing her student’s rate of reading. She has two fluency programs that she believes may work with Bob. She implements the two different programs on alternate days over 19 days. After the completion of the experiment, she is confident that intervention #1 will achieve better results for improving Bob’s reading skills

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