In the Overall Performance tab, located in the Assessment Analysis tab, we assign student achievement into levels using the chosen Performance Band. Each Assessment has a default performance band, but you can also change the displayed performance band in the application.
We found that those performance bands do very well at describing OVERALL achievement -- that is, the overall score a student received on an assessment.
But in the Item Analysis, Standards Analysis, and Rubric Analysis tabs, the "student achievement" is not based on the overall score on the assessment, but instead on how the student did on a particular question (item analysis), standard (standards analysis), or for items graded with a rubric (rubric analysis).
For Item Analysis in particular this was a factor because unless an item has "partial credit" grading, students had all (100%) or none (0%). For Standards and Rubric analysis there was a similar problem if there were not many questions within each standard or on a rubric.
Our solution was to continue to use Performance Bands for overall achievement but to use hard-coded percentage-based bands for Item Analysis, Standards Analysis, and Rubric Analysis.
Standards Analysis and Rubric Analysis: quintiles, as follows:
Top Quintile: 80 - 100
Fourth Quintile: 60 - 80
Third Quintile: 40 - 60
Second Quintile: 20 - 40
Bottom Quintile: 0 - 20
Item Analysis: A three-level band, as follows:
Full (credit): 100
Partial (credit): 1 - 99