The two sets of norms (Individual Percentile Rank and the Norm Scores) may differ slightly as they have been based on different random samples of students from each region. This slight variation provides greater generalization to the outcomes and should remind teachers and administrators that all measurement contains some minor amount of error and score values are best represented in confidence bands (the range of scores within which we can be confident a specific score is present). Note also that the IPRs (Individual Percentile Rank) are sampled proportionately by region, not by race, ethnicity, or gender.
Both are equally good so the decision on which one to use is left to your preference.
Chapter 2 (p. 3) of the easyCBM Technical Manual (Technical Report #1408) is a summary of the norming methods and results and can be found here: http://www.brtprojects.
A longer more detailed description of the norms can be found here: http://www.brtprojects.
If you’re interested in reviewing the details of our research, please visit our website, http://www.brtprojects.org/publications/technical-reports. We have numerous technical reports that detail the various elements, design, and methodology that go into our research projects.