The development of a Functional Math Inventory in Rasch framework: An integrated approach for constructing instruments for assessing students with severe disabilities

A literature review disclosed an emergent need for effective instructionally relevant instruments to assist educators in working with students with severe disabilities. Very few such instruments exist because neither the Developmental nor the Functional models provide an appropriate theoretical basis for their construction. An instrument for use in both assessing and training individuals with severe disabilities is difficult to develop because it needs to consider at least three criteria. (1) The instrument must take wide individual differences into account and must employ observation as a scoring means. (2) Items achieved or missed by an individual must be able to determine the individual's ability level and can be transferred into sequential and longitudinal steps for program planning. (3) The instrument must be applicable in various life domains as well as physical settings.;This study proposed an integrated developmental and functional model as the theoretical basis and the Rasch model as the statistical framework for constructing and calibrating an instrument for assessing students with severe disabilities. Applying the integrated model, the Functional Math Inventory (FMI) was developed for assessing functional math skills as well as for serving as a curriculum guide for training students with severe disabilities.;Ten teachers who worked closely with students with severe disabilities participated in the construction of the FMI item pool. The item pool was calibrated with the SCALE program on 40 subjects who had moderate to severe needs and were non-randomly selected from students at the Perkins School for the Blind in Massachusetts. The Rasch analysis resulted in evidence that supported the FMI's reliability and construct validity.;The calibrated FMI consists of 98 items with three difficulty levels, and it targets three major areas of math skills: Pre-math, Basic Math and Essential Skills. Each of the FMI items is scored in 4 unique life domains that are defined as 4 subitems. This design ensures a consistency of performance of the individuals evaluated.