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The Impact of Item Model Parameter Variations on Person Parameter Estimation in Computerized Adaptive Testing With
1Department of Human Development and Quantitative Methodology, University of Maryland, College Park, MD, USA.
Ignoring sibling item variations in psychometric testing has minimal impact on score accuracy but can introduce bias. Increasing test length can compensate for larger variations, with similar effects in linear and adaptive testing.
Area of Science:
- Psychometrics
- Educational Measurement
- Item Response Theory
Background:
- Sibling items from automatic generation share similar psychometric properties but have variations.
- Ignoring these variations simplifies computation but may affect scoring accuracy.
- Understanding the impact of within-family variance is crucial for accurate person parameter estimation.
Purpose of the Study:
- To explore the impact of item model parameter variations (within-family variance) on person parameter estimation.
- To investigate if test length can compensate for larger within-model variance.
- To determine if item pool characteristics influence the scoring impact of within-family variance.
- To compare these effects in linear versus Computerized Adaptive Testing (CAT).
Main Methods:
- Data generation using a related sibling model, assuming an identical sibling model for scoring.
- Manipulation of factors including test length, within-model variation size, and item model pool characteristics.
- Analysis of standard error, correlation between true and estimated scores, Root Mean Square Error (RMSE), and bias.
Main Results:
- Increased within-family variance did not significantly affect the standard error of scores.
- Test length compensated for larger within-model variance regarding score correlation and RMSE.
- Bias in scores was observed, tending towards the center, and was not compensated by test length.
- Computerized Adaptive Testing (CAT) showed similar results to linear tests but with higher efficiency.
Conclusions:
- While standard errors are stable, ignoring within-family variance can lead to biased ability estimates.
- Balanced item model pools are recommended to mitigate bias by canceling out 'fake-easy' and 'fake-difficult' item effects.
- Test length is a viable strategy to manage the impact of within-family variance on score accuracy.
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