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D.9: Apply single-case experimental designs.

Free practice questions for this part of the BCBA, with an explanation for every option.

A BCBA is using a multiple-baseline-across-participants design to evaluate functional communication training with three children. FCT has started for Child 1, and Child 1's problem behavior is dropping. When should FCT be introduced for Child 2?
  1. A. After Child 1 shows a clear, stable change and Child 2's baseline remains stable and unaffected
    Correct. Staggering by data, so that the next tier gets intervention only after the first shows a clear effect and the next tier stays stable, provides verification and replication.
  2. B. After Child 2's problem behavior starts decreasing on its own during baseline
    Incorrect. Starting treatment while baseline is already improving confounds the evaluation. A stable baseline is needed first.
  3. C. On a preset calendar date, whatever the data show
    Incorrect. Phase changes in single-case designs should depend on the data, such as stability and clear effects, not on an arbitrary date.
  4. D. At the same time as Child 1, to save time
    Incorrect. Starting at the same time removes the staggered comparison, so changes could be blamed on a common outside variable.
A BCBA is using a changing-criterion design to increase the minutes a client exercises on a stationary bike. Which plan would most strengthen experimental control?
  1. A. Vary the length of the phases and the size of the criterion changes, and include a temporary return to an earlier (lower) criterion
    Correct. When behavior tracks criteria that vary in length and size, including a reversal to a previous criterion, that strongly shows the criteria, not maturation or practice, control responding.
  2. B. Set the final goal from the first session, so the client knows the target
    Incorrect. A single fixed goal removes the stepwise criteria the design depends on for showing control.
  3. C. Change the criterion only when the client asks for a new goal
    Incorrect. Letting the client decide when criteria change means changes no longer depend on stable responding at each criterion, which weakens the logic of the design.
  4. D. Raise the criterion by exactly 5 minutes every 3 sessions, so the phases are uniform
    Incorrect. Uniform, predictable phase lengths and step sizes make it harder to rule out that behavior is just following a time-based trend.
A BCBA in an early intervention clinic collects 4 baseline sessions on a 4-year-old's tantrum duration: 12, 2, 18, and 6 minutes, with no clear trend. The tantrums are not dangerous. What should she do next?
  1. A. Continue baseline until responding is stable enough to predict future levels
    Correct. Steady-state responding allows prediction. Without it, any later change cannot be clearly attributed to the intervention. Because the behavior is not dangerous, extending baseline (and looking for sources of the variability) is appropriate.
  2. B. Start the intervention now, because 3 or more baseline points are always enough
    There is no fixed minimum number of baseline points. What matters is whether the data are stable enough to predict what would happen without treatment.
  3. C. Average the 4 sessions and use the mean as the baseline level
    Averaging hides the variability and does not create a stable baseline to predict from.
  4. D. Switch to a changing-criterion design to reduce the variability
    Changing design does not solve unstable baseline data. A changing-criterion design also needs a stable baseline.

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