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Rasch analysis of the School Function Assessment provides additional evidence for the internal validity of the
Jeng-Liang Hwang1, Patricia L Davies
1Department of Occupational Therapy, California State University, Dominguez Hills, USA. ehwang@csudh.edu
Objective:
The internal construct validity of the School Function Assessment (SFA) was determined by examining its unidimensionality and hierarchical structure.
Method:
The SFA was completed for 64 elementary school children (35 with disabilities, 29 without disabilities). Data were examined through Rasch analysis.
Results:
The majority of test items (252 of 266) within the Activity Performance Scales met the criterion set for Rasch goodness-of-fit statistics. All but three scales were found to be unidimensional, measuring a single construct. Item difficulty analysis yielded a hierarchical structure of the scales similar to the existing item layout of the SFA.
Conclusion:
Internal validity was supported for 15 of the 18 Activity Performance scales. Each scale is psychometrically sound in measuring a specific functional task. The reliable hierarchical pattern of the assessment helps anticipate and document the student's progress in functional performance from easier to more difficult school tasks.
