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A research assistant is calculating difference scores for a dependent-samples -test. For the first 10 participants, they subtract Pretest scores from Posttest scores. For the remaining 10 participants, they subtract Posttest scores from Pretest scores because they want all difference scores to be positive. Identify the error in this application and explain how it must be corrected.
Question: A research assistant is calculating difference scores for a dependent-samples -test. For the first 10 participants, they subtract Pretest scores from Posttest scores. For the remaining 10 participants, they subtract Posttest scores from Pretest scores because they want all difference scores to be positive. Identify the error in this application and explain how it must be corrected.
Sample answer: The error is that the subtraction order was not applied consistently across all participants. To correct this, the research assistant must choose a single direction of subtraction (e.g., Posttest minus Pretest) and apply it to every participant uniformly.
Key points:
- The subtraction order was applied inconsistently between participants.
- Consistency in the direction of subtraction is required across all participants.
- Correcting the error requires choosing one subtraction direction and applying it uniformly to all data points.
Feedback: Ensure the student identifies the inconsistency in subtraction order as the primary error and specifies that the direction of subtraction must be identical across all participants.
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Research Methods in Psychology - 4th American Edition @ KPU
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A research assistant is calculating difference scores for a dependent-samples -test. For the first 10 participants, they subtract Pretest scores from Posttest scores. For the remaining 10 participants, they subtract Posttest scores from Pretest scores because they want all difference scores to be positive. Identify the error in this application and explain how it must be corrected.