Develops an approach for advance estimation of user charges based on information actually retrieved by searching numeric databases, and defines a method for query cardinality estimation. Based on the relational data model, which uses relational algebra, this method uses formal file descriptions to describe the database files. (LRW)

The use of restricted item response models to test hypotheses regarding item difficulty ordering and slope uniformity was demonstrated in a study in which 597 algebra students were asked to solve word problems reflecting various types of cognitive processing. Benefits and limitations of the procedures are discussed. (SLD)