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Define the interrupted time-series design and explain its structure as a variant of the pretest-posttest design. In your explanation, highlight the specific operational difference between this design and a simple pretest-posttest design, and state the main advantage this difference provides to researchers.

Question: Define the interrupted time-series design and explain its structure as a variant of the pretest-posttest design. In your explanation, highlight the specific operational difference between this design and a simple pretest-posttest design, and state the main advantage this difference provides to researchers.

Sample answer: An interrupted time-series design is a quasi-experimental approach and a variant of the pretest-posttest design where a researcher takes multiple measurements of a dependent variable at regular intervals (a time series) both before and after a treatment is introduced. The treatment effectively 'interrupts' these measurements. Unlike a simple pretest-posttest design, which relies on a single measurement before and a single measurement after the treatment, the interrupted time-series design includes multiple pretest and posttest measurements. The primary advantage of this structure is that the multiple measurements allow researchers to better distinguish the actual effect of the intervention from normal variation.

Key points:

  • Defines the interrupted time-series design as a quasi-experimental approach and variant of the pretest-posttest design.
  • Explains that measurements of the dependent variable are taken at regular intervals (time series) both before and after the treatment.
  • Contrasts the multiple measurements of a time-series design with the single before-and-after measurements of a simple pretest-posttest design.
  • Identifies the main advantage as the ability to distinguish the actual treatment effect from normal variation.

Rubric: To receive full credit, the response must accurately define the interrupted time-series design, explain its relationship to the pretest-posttest design, identify the difference in the number of measurements (multiple vs. single), and explain how this helps distinguish treatment effects from normal variation.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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