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Based on the characteristics of a one-group pretest-posttest design, explain why the school psychologist's conclusion is difficult to make with certainty. What specific feature is missing from this study design that makes it vulnerable to alternative explanations?
Case context: A school psychologist implements a new reading intervention program for a group of struggling readers. The psychologist measures the students' reading speeds at the beginning of the semester, administers the new intervention for eight weeks, and then measures their reading speeds again at the end of the intervention. The psychologist notes a significant increase in reading speeds and concludes with certainty that the new intervention was effective.
Question: Based on the characteristics of a one-group pretest-posttest design, explain why the school psychologist's conclusion is difficult to make with certainty. What specific feature is missing from this study design that makes it vulnerable to alternative explanations?
Sample answer: The psychologist's conclusion is difficult to make with certainty because this study uses a one-group pretest-posttest design, which lacks a control group. Because there is no control group to compare against, the study is highly vulnerable to alternative explanations and threats to internal validity. Other unmeasured factors, rather than just the intervention, might have caused the students' reading speeds to improve during those eight weeks.
Key points:
- The study uses a one-group pretest-posttest design.
- Conclusions about the treatment's effectiveness are difficult to make with certainty.
- The design lacks a control group.
- The absence of a control group leaves the study highly vulnerable to alternative explanations and threats to internal validity.
Rubric: The response must identify that the conclusion is vulnerable because the study design lacks a control group. It should explain that this absence makes the study highly susceptible to alternative explanations and threats to internal validity.
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Research Methods in Psychology - 4th American Edition @ KPU
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Example of a One-Group Pretest-Posttest Design
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