New Item response Theory-based Dizziness Impact Measures Were Reliable, Valid, and Efficient

Research Objectives: Calibrate items from the Dizziness Handicap Inventory (DHI) patient-reported outcome measure (PROM) to create an item response theory (IRT)-based item bank and assess its reliability, validity, and efficiency using computerized adaptive test (CAT) and short form (SF) administration modes.

Design: A retrospective cohort including data from patients assessed for dizziness.

Setting: Outpatient rehabilitation.

Participants: Total cohort consisted of 28,815 adult patients [69% female; mean age (SD) 60 (18)] treated in 976 clinics from 49 states (USA) for either vertigo, brain injury, or neck impairments who responded to all 25 DHI items at intake.

Interventions: Not applicable.

Main Outcome Measures: IRT model assumptions of local independence, unidimensionality, item fit, and absence of differential item functioning (DIF) were evaluated. CAT and SF T-scores (mean=50, SD=10) were assessed for reliability, validity, and administration efficiency. Score known-groups validity was assessed for the ability to discriminate among patient groups by demonstrating expected differing levels of dizziness impact. Floor and ceiling effects were assessed, and responsiveness was evaluated using an effect-size statistic.

Results: Three unidimensional item sets were identified, creating 3 distinct PROMs to assess functional (DF; 13 items), positional (DP; 4 items), and emotional (DE; 6 items) status (higher score=lower impact). Each item fit its IRT model. Reliability estimates were 0.72 to 0.92. Except for DIF by age group for DF and DE, no items were flagged for DIF, with negligible DIF impact. Scores discriminated between patient groups in clinically expected ways. Floor and ceiling effects were acceptable ( < 15%) excepting a floor effect for the positional PROM (21.4%). Effect sizes were large (>0.8). A CAT was developed for DF, administering an average of 8.3 items (median=9, range 5 to 10).

Conclusions: The 3 dizziness PROMs demonstrated moderate to high reliability, were valid, highly responsive to change; thus, they are suitable for routine clinical administration.

Author(s) Disclosures: Dr. Kallen consults for Net Health Systems, Inc., that owns the Focus on Therapeutic Outcomes (FOTO) Patient Outcomes system that gathers and manages the data analyzed. The authors have no other conflicts to declare.