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Explain the structure of an AB design in single-subject research, identify the larger class of research design it is structurally similar to when applied to one participant, and outline the major limitation that impacts its internal validity.

Question: Explain the structure of an AB design in single-subject research, identify the larger class of research design it is structurally similar to when applied to one participant, and outline the major limitation that impacts its internal validity.

Sample answer: An AB design is a single-subject research structure containing exactly two phases: an initial baseline phase (A) followed by a single treatment phase (B). Structurally, this design functions similarly to an interrupted time-series design applied to an individual participant. The main limitation of the AB design is its susceptibility to confounding variables. If the dependent variable changes when the treatment is introduced, it is unclear whether the treatment itself or an extraneous coincidental variable caused the change, resulting in lower internal validity than reversal designs.

Key points:

  • The AB design consists of a baseline phase (A) followed by a treatment phase (B).
  • It is structurally similar to an interrupted time-series design applied to a single participant.
  • It has a significant limitation regarding susceptibility to confounding or extraneous variables.
  • It yields lower internal validity compared to reversal designs because causal relationships cannot be clearly established.

Rubric: To receive full credit, the response must recall: 1) The two phases of the AB design (baseline A, treatment B). 2) Its similarity to an interrupted time-series design applied to a single participant. 3) Its primary limitation: susceptibility to confounding/extraneous variables causing changes in the dependent variable, leading to lower internal validity compared to reversal designs.

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Updated 2026-05-26

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KPU

Research Methods in Psychology - 4th American Edition @ KPU

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