Construct Validity of the School Outcomes Measure (SOM) When Used With Secondary Students Receiving School-Based Therapy Open Access

The purpose of this study was to determine the construct validity of the School Outcomes Measure (SOM) when used with secondary school students who receive school-based occupational therapy and physical therapy services.

Research questions included “Do items in the SOM contribute to a unidimensional construct of school-related function in a sample of secondary school students?” and “Do the current SOM items capture the school-related abilities of secondary school students?”

Increasingly, professionals are expected to provide evidence supporting the effectiveness of their interventions. Unfortunately, no established valid and reliable tool exists to measure outcomes of occupational therapy and physical therapy services provided to secondary students with disabilities. The SOM, a minimal data set, is specifically designed to measure school-related outcomes, but validity studies have been based on preschool and elementary school children. If the SOM is to be a useful tool for collecting data on all students who receive school-based occupational therapy and physical therapy services, further testing of the construct validity with a secondary school population is warranted.

The SOM consists of 41 items and seven subscales that are scored on a 6-point scale (1 = total assistance, 2 = maximum assistance, 3 = moderate assistance, 4 = minimal assistance, 5 = supervision, 6 = independent) to rate students’ abilities. The current subscales rate self-care, mobility, assuming a student’s role (preschool/elementary or secondary students), expressing learning, and behavior. The SOM was uploaded into Survey Monkey so participants could access it from a home or work computer.

We used a prospective cross-sectional descriptive study design. We recruited a convenience sample of respondents from a direct mailing to 250 randomly selected members of the American Occupational Therapy Association’s School System Special Interest Section, research announcements links on electronic bulletin boards, and electronic mailing lists for pediatric and school-based occupational therapists and physical therapists.

Thirty-one practicing school-based occupational therapists (n = 10) and physical therapists (n = 21) from 15 states collected SOM data on 108 secondary school students.

We conducted the Rasch analysis and used Winsteps 3.75.0 software to determine dimensionality and difficulty hierarchy of items, by examining fit statistics and principal-components analysis of standardized residuals. We investigated both person reliability estimates and item reliability estimates and determined whether or not items were well targeted, by comparing person ability estimates with item difficulty estimates in logits.

The Rasch analysis revealed that the SOM was multidimensional and identified three separate subscales: Mobility, Manipulation in Learning, and Behavior. Items in all three subscales fit the Rasch model, formed predictable hierarchies, and showed limited redundancy in terms of item difficulty. The loading on other items were low, supporting the construct validity of the scales. The identification of three distinct subscales offers increased potential for the SOM to evaluate school-based outcomes.

Our results suggest that the SOM distinguishes not only among students’ physical and manipulation ability levels in the school setting, but also among their behavior. The fit statistics results supported item hierarchy, suggesting the items may be used to measure change, and each scale can be used independently.

The SOM offers occupational therapists and physical therapists a valid tool for systematically collecting data on the Mobility, Manipulation in Learning, and Behavior abilities of secondary students with whom they work.