Simulated computerized adaptive tests for measuring functional status were efficient with good discriminant validity in patients with hip, knee, or foot/ankle impairments

Abstract 

Background and Objective

To develop computerized adaptive tests (CATs) designed to assess lower extremity functional status (FS) in people with lower extremity impairments using items from the Lower Extremity Functional Scale and compare discriminant validity of FS measures generated using all items analyzed with a rating scale Item Response Theory model (θ_IRT) and measures generated using the simulated CATs (θ_CAT).

Methods

Secondary analysis of retrospective intake rehabilitation data.

Results

Unidimensionality of items was strong, and local independence of items was adequate. Differential item functioning (DIF) affected item calibration related to body part, that is, hip, knee, or foot/ankle, but DIF did not affect item calibration for symptom acuity, gender, age, or surgical history. Therefore, patients were separated into three body part specific groups. The rating scale model fit all three data sets well. Three body part specific CATs were developed: each was 70% more efficient than using all LEFS items to estimate FS measures. θ_IRT and θ_CAT measures discriminated patients by symptom acuity, age, and surgical history in similar ways. θ_CAT measures were as precise as θ_IRT measures.

Conclusion

Body part-specific simulated CATs were efficient and produced precise measures of FS with good discriminant validity.

Keywords: Computerized adaptive testing, Item response theory, Lower Extremity Functional Scale, Rehabilitation