Based on the provided context, diagnose whether the researcher can definitively conclude that the reading intervention caused any observed differences in posttest reading scores, and justify your answer by explaining how the classroom selection choices affect the study's validity.
Case context: A researcher evaluates a new reading intervention across two pre-existing fifth-grade classrooms. She selects two classrooms in the same school where both teachers have similar teaching styles, and the students have similar baseline reading scores. After the intervention is implemented in one classroom, the researcher compares the reading scores of both classes at the end of the year.
Question: Based on the provided context, diagnose whether the researcher can definitively conclude that the reading intervention caused any observed differences in posttest reading scores, and justify your answer by explaining how the classroom selection choices affect the study's validity.
Sample answer: The researcher cannot definitively conclude that the reading intervention caused the differences in reading scores because the study lacks true random assignment of students to conditions. Although selecting classrooms from the same school with similar baseline scores and teacher styles improves the study's internal validity by eliminating major known confounds, unmeasured confounding variables (such as individual student motivation or parental involvement) may still influence the outcomes and explain the differences.
Key points:
- Diagnose that the researcher cannot make definitive causal claims.
- Explain that the study lacks true random assignment.
- Acknowledge that selecting similar comparison groups (same school, similar baseline scores and teacher styles) improves internal validity by eliminating major known confounds.
- Understand that unmeasured confounding variables may still influence the final outcomes.
Rubric: The student must diagnose that a causal claim is not justified. They must comprehend and explain that matching the classrooms on key characteristics (school, baseline scores, teacher style) improves internal validity by reducing major confounds, but the lack of true random assignment means unmeasured confounding variables could still influence outcomes.
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Research Methods in Psychology - 4th American Edition @ KPU
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