Structured interview to improve the reliability and psychometric integrity of the Disability Rating Scale

Abstract

Objectives: To (1) develop a standardized interview for telephone administration, (2) assess the psychometric properties of this interview format (Disability Rating Scale-Postacute Interview [DRS-PI]), and (3) identify additional items to reduce skew.

Design: Prospective cohort assessment study.

Setting: Not applicable.

Participants: Participants (N=406; 287 individuals with traumatic brain injury [TBI], 119 caregivers) in the U.S. TBI Model Systems national database during 1- to 20-year telephone follow-up.

Interventions: Not applicable.

Main outcome measures: Original Disability Rating Scale (DRS) and DRS-PI variations. DRS-PI questions were developed by consensus of the study investigators; item scores were derived from responses to questions by algorithm. Unnecessary questions were pruned.

Results: The DRS-PI correlated highly with the original DRS (intraclass correlation, .91) and demonstrated satisfactory construct validity and internal consistency (person separation/reliability, 2.51/.86; item separation/reliability, 16.72/1.00; Cronbach α=.83). Both versions showed substantial skew. For the original DRS, 42% of scores were 0 or 1; for DRS-PI, 44%. Adding several items to the DRS-PI including actual employment status further improved its psychometric properties (person separation/reliability, 3.10/.91; item separation/reliability, 21.42/1.00; Cronbach α=.92) and reduced skew. For the Expanded DRS-PI, 18% of scores were 0 or 1.

Conclusions: The DRS-PI provides an efficient method to ensure standardized administration of, and correlates highly with, the original DRS. The addition of several new items including actual employment status mitigates skew in postacute samples.