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Treatment outcomes for students with learning disabilities: how important are internal and external validity?
1Educational Psychology and Special Education, School of Education, University of California, Riverside 92521, USA.
Journal of Learning Disabilities
|October 27, 2004
Summary
Research on students with learning disabilities shows that flaws in study design, like teacher effects and varied measures, significantly impact intervention outcomes. Underreporting data also inflates results, affecting real-world application.
Area of Science:
- Educational Psychology
- Special Education Research
- Research Methodology
Background:
- Intervention research for students with learning disabilities (LD) is crucial for evidence-based practice.
- Assessing the true magnitude of intervention effects requires rigorous examination of study validity.
- Previous studies have not comprehensively analyzed how validity violations influence effect sizes in LD research.
Purpose of the Study:
- To analyze how violations in internal and external validity affect the magnitude of experimental intervention outcomes for students with LD.
- To identify specific validity threats that significantly alter treatment outcome measures.
- To investigate the impact of underreported study characteristics on the perceived effectiveness of interventions.
Main Methods:
- Analysis of experimental intervention studies involving students with learning disabilities.
- Examination of validity violations including teacher effects, criterion levels, measure consistency, sample homogeneity, and units of analysis.
- Regression analysis to determine the variance in effect size attributable to high-risk validity variables.
Main Results:
- Treatment outcomes were significantly affected by teacher effects, criterion levels, experimental measures, pretest-posttest measure differences, age heterogeneity, and incorrect units of analysis.
- Underreporting of ethnicity, locale, psychometric data, and teacher applications positively inflated outcome magnitudes.
- Composite scores of high-risk variables accounted for 16% of the total variance in effect size.
Conclusions:
- Specific methodological flaws and underreporting in intervention research substantially distort the reported effectiveness of interventions for students with LD.
- Researchers must address validity threats and improve reporting standards to ensure accurate interpretation and application of findings.
- Improved methodological rigor and transparent reporting are essential for advancing evidence-based practices in special education.
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