Short form of the Dizziness Handicap Inventory: construction and validation through Rasch analysis

Abstract

A new item response scale is presented, which measures the severity of self-reported balance deficits. The scale, DHIsf, is a short form of the Dizziness Handicap Inventory. The scale was constructed and validated by Rasch analysis. Rasch analysis was applied to rescore or remove any items misfitting, redundant, or off-target, until an optimal instrument was obtained. The 25-item, 3-level Dizziness Handicap Inventory was, thus, reduced to the 13-item, 2-level DHIsf. The retained items explore the domains of eye/head movements, full body activities, and mood alterations. Data were collected from 55 outpatients (63 +/- 13 yr; 43 females) attending otoneurological rehabilitation referral at a general hospital because of complaints of dizziness or imbalance. They were fully independent in ambulation and showed no evidence of major neurological or orthopedic diseases. Objective tests included brain computed tomography, sovraaorctic Doppler sonography, craniocorpography, static posturography, and nystagmography. The findings were categorized as pathologic, borderline, or normal. At least one examination was borderline or abnormal in 42 patients. The DHIsf was well targeted on this sample, with a mean score of 5.7/13 (standard deviation, 2.8; median, 5; range, 1-13). The Rasch statistics showed that the 13 items evenly fitted a hierarchy of difficulty within a homogeneous construct. A moderate but significant variance explanation of DHIsf measures was provided by a two-way analysis of variance model, with craniocorpography and nystagmography as independent categorical variables (r2 = 0.15; P = 0.018). When the clinical tests were individually taken into account, their outcome (dichotomized as abnormal v borderline or normal) could not be predicted by either of the DHIsf measures or raw scores (logistic regression). The DHIsf compares favorably with the original Dizziness Handicap Inventory, shows some consistency with the instrumental findings, and provides original information on the severity of imbalance syndromes, as it is seen from the patient's perspective.