How Accurate are the STAR National Percentile Rank Scores for Individual Students?--An interpretive guide.

Version 1.0    August, 1999

David Rogosa
Stanford University

Note: Current Version 1.0 is likely to be updated in response to comments

The goal here is to apply some common-sense descriptions of accuracy to the numbers–National Percentile Rank Scores from the Stanford 9–that are used to indicate student achievement in the STAR Parent Report and Student Report.

This guide has nothing to do with the STAR Augmentation test items introduced in 1999.
Basic information on the full STAR testing program and score reports is available from CDE: STAR Information and Assistance Packets
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Many informal statements and references in this Accuracy Guide are given explicit, mathematical definition in two CRESST Technical Reports released in concert with this Accuracy Guide.
So for those who might be interested in technical details and underpinnings for these calculations, the two related CRESST Technical Reports are

1. Accuracy of Individual Scores Expressed in Percentile Ranks: Classical Test Theory Calculations
2. Accuracy of Year-1, Year-2 Comparisons Using Individual Percentile Rank Scores: Classical Test Theory Calculations
In addition, if there is interest, I may prepare an additional report on the details of constructing these specific calculations for Stanford 9 using test publisher information.