ABA Exam Coach

D.3: Identify threats to internal validity (e.g., history, maturation).

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

During the intervention phase of an AB design targeting elopement, the client's physician starts a new medication. Elopement drops sharply in the same week. What threat to internal validity is most evident?
  1. A. Regression to the mean
    Incorrect. Regression to the mean is extreme scores drifting toward average. A new medication starting at the same time is a separate kind of confound.
  2. B. History
    Correct. History is an uncontrolled event outside the study, here a medication change, that happens at the same time as the independent variable and could explain the change.
  3. C. Maturation
    Incorrect. Maturation means gradual changes within the person over time, such as development or aging, not a discrete outside event.
  4. D. Multiple-treatment interference
    Incorrect. Multiple-treatment interference is about the effects of the study's own planned treatments influencing each other, not an outside medical change.
A BCBA runs a 6-month AB evaluation of a naturalistic language intervention with a 26-month-old. Spontaneous two-word phrases rise slowly and steadily across the intervention phase. Which threat to internal validity is most important to rule out?
  1. A. Sequence effects
    Incorrect. Sequence effects need more than one treatment condition presented in some order. An AB design has only one intervention.
  2. B. Maturation
    Correct. In a very young child over a long period, normal developmental change could produce gradual language gains whether or not the intervention was in place, and an AB design cannot rule that out.
  3. C. Reactivity to the observer's presence
    Incorrect. Reactivity is possible, but it usually shows up as a fairly quick change once observation begins, not as gradual gains over months.
  4. D. Observer drift
    Incorrect. Observer drift is a measurement problem. Nothing in the scenario suggests the observers' scoring changed.
Over a 10-week study, two RBTs collecting data on 'disruptive vocalizations' gradually begin scoring quieter sounds they would not have counted earlier. They still agree with each other at 90% or above. Which statement best describes this threat?
  1. A. History: an outside event caused the behavior to change
    Incorrect. The change described is in the observers' scoring, not in an outside event acting on the client.
  2. B. Maturation: the client's vocalizations naturally changed across 10 weeks
    Incorrect. The scenario says the observers' scoring changed, not the client's behavior.
  3. C. Observer drift (instrumentation): measurement changes over time, so data may show change that did not occur in behavior
    Correct. Observer drift is an unintended change in how observers apply the response definition over time. It threatens validity because the data may change when the behavior has not.
  4. D. High IOA confirms the data are accurate, so no threat exists
    Incorrect. High IOA shows the observers are consistent with each other, not that they are accurate. Two observers can drift together, so periodic retraining against the original definition is needed.

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