Explain the primary advantage of utilizing an interrupted time-series design over a simple one-group pretest-posttest design when evaluating a psychological intervention. In your response, specifically address the role of measurement frequency and how it affects a researcher's ability to draw conclusions about the intervention's effectiveness.
Question: Explain the primary advantage of utilizing an interrupted time-series design over a simple one-group pretest-posttest design when evaluating a psychological intervention. In your response, specifically address the role of measurement frequency and how it affects a researcher's ability to draw conclusions about the intervention's effectiveness.
Sample answer: The primary advantage of an interrupted time-series design over a simple one-group pretest-posttest design is its ability to account for normal, ongoing fluctuations in the dependent variable. By taking multiple measurements before and after the intervention, researchers can establish a baseline trend. A simple pretest-posttest design only measures the dependent variable once before and once after, which cannot distinguish a genuine treatment effect from normal, week-to-week variations in the data.
Key points:
- Identifies that the interrupted time-series design collects multiple measurements both before and after an intervention.
- Explains that multiple measurements are used to establish a baseline trend.
- Contrasts the multiple measurements of a time-series design with the single pretest and posttest measurements of a pretest-posttest design.
- Explains how a baseline trend accounts for normal, ongoing fluctuations (e.g., week-to-week variation) in the dependent variable.
- Notes that the design prevents researchers from falsely attributing normal fluctuations to the treatment effect.
Rubric: The response must clearly state that the interrupted time-series design uses multiple measurements before and after the intervention to establish a baseline trend. The response must also explain that this baseline trend allows researchers to account for normal, ongoing fluctuations (such as week-to-week variation) in the dependent variable, whereas a simple pretest-posttest design only collects single measurements and cannot distinguish genuine treatment effects from these normal variations.
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Example of an Interrupted Time-Series Design: Student Absences
What is a primary advantage of the interrupted time-series design over a simple one-group pretest-posttest design?
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A university counseling director collected 14 weekly measurements of students' self-reported anxiety—7 weeks before a new stress-management workshop and 7 weeks after—using an interrupted time-series design. She must now evaluate whether the post-workshop drop in anxiety is a genuine treatment effect or merely normal semester variation. Rank the following analytical steps in the order that best supports a valid, evidence-based conclusion.
Explain the primary advantage of utilizing an interrupted time-series design over a simple one-group pretest-posttest design when evaluating a psychological intervention. In your response, specifically address the role of measurement frequency and how it affects a researcher's ability to draw conclusions about the intervention's effectiveness.
Based on the provided context, identify the major limitation of the psychologist's research design in terms of measurement frequency. Then, explain how transitioning to an interrupted time-series design would address this limitation and why it would lead to a more valid conclusion.
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