RESUMO
Background/Objectives: The Dysphagia Handicap Index (DHI) is commonly used in oropharyngeal dysphagia (OD) research as a self-report measure of functional health status and health-related quality of life. The DHI was developed and validated using classic test theory. The aim of this study was to use item response theory (Rasch analysis) to evaluate the psychometric properties of the DHI. Methods: Prospective, consecutive patient data were collected at dysphagia or otorhinolaryngology clinics. The sample included 256 adults (53.1% male; mean age 65.2) at risk of OD. The measure's response scale, person and item fit characteristics, differential item functioning, and dimensionality were evaluated. Results: The rating scale was ordered but showed a potential gap in the rating category labels for the overall measure. The overall person (0.91) and item (0.97) reliability was excellent. The overall measure reliably separated persons into at least three distinct groups (person separation index = 3.23) based on swallowing abilities, but the subscales showed inadequate separation. All infit mean squares were in the acceptable range except for the underfitting for item 22 (F). More misfitting was evident in the Z-Standard statistics. Differential item functioning results indicated good performance at an item level for the overall measure; however, contrary to expectation, an OD diagnosis presented only with marginal DIF. The dimensionality of the DHI showed two dimensions in contrast to the three dimensions suggested by the original authors. Conclusions: The DHI failed to reproduce the original three subscales. Caution is needed using the DHI subscales; only the DHI total score should be used. A redevelopment of the DHI is needed; however, given the complexities involved in addressing these issues, the development of a new measure that ensures good content validity may be preferred.
RESUMO
The Swallowing Quality of Life questionnaire (SWAL-QOL) is widely used clinically and in research to evaluate quality of life related to swallowing difficulties. It has been described as a valid and reliable tool, but was developed and tested using classic test theory. This study describes the reliability and validity of the SWAL-QOL using item response theory (IRT; Rasch analysis). SWAL-QOL data were gathered from 507 participants at risk of oropharyngeal dysphagia (OD) across four European countries. OD was confirmed in 75.7% of participants via videofluoroscopy and/or fiberoptic endoscopic evaluation, or a clinical diagnosis based on meeting selected criteria. Patients with esophageal dysphagia were excluded. Data were analysed using Rasch analysis. Item and person reliability was good for all the items combined. However, person reliability was poor for 8 subscales and item reliability was poor for one subscale. Eight subscales exhibited poor person separation and two exhibited poor item separation. Overall item and person fit statistics were acceptable. However, at an individual item fit level results indicated unpredictable item responses for 28 items, and item redundancy for 10 items. The item-person dimensionality map confirmed these findings. Results from the overall Rasch model fit and Principal Component Analysis were suggestive of a second dimension. For all the items combined, none of the item categories were 'category', 'threshold' or 'step' disordered; however, all subscales demonstrated category disordered functioning. Findings suggest an urgent need to further investigate the underlying structure of the SWAL-QOL and its psychometric characteristics using IRT.
