Title:
Validation of the Swedish M. D. Anderson Dysphagia Inventory (MDADI) in patients with head and neck cancer and neurologic swallowing disturbances.

Abstract:
The aim of this study was to validate the Swedish version of the dysphagia-specific quality-of-life questionnaire, the M. D. Anderson Dysphagia Inventory (MDADI). Patients with oropharyngeal dysphagia due to neurologic disease (n = 30) and head and neck (H&N) cancer patients with post-treatment subjective dysphagia (n = 85) were compared to an age- and gender-matched nondysphagic control group (n = 115). A formal forward-backward translation was performed and followed international guidelines. Validity and reliability were tested against the Short-Form 36 (SF-36) and Hospital Anxiety and Depression Scale (HADS). Internal-consistency reliability was calculated by means of Cronbach's α coefficient. Test-retest reliability was assessed by intraclass correlation (ICC). Convergent and discriminant validity were assessed by correlations between MDADI, SF-36, and HADS. Known-group validity was examined and statistically tested. Of 126 eligible patients, 115 agreed to participate (response rate = 91.3%). The age of the participants ranged between 37 and 92 years. Most of the MDADI items showed good variability and only minor floor or ceiling effects in solitary items were found. The internal-consistency reliability (Cronbach's α) of the MDADI total score was 0.88 (after correction for systematic errors in the subjects' responses to two reversed questions). All estimates reached over the satisfactory >0.70 reliability standard for group-level comparison. ICC ranged between 0.83 and 0.97 in the test-retest. The mean MDADI total score was 66.9 (SD = 14.7) for the H&N cancer patients, 65.0 (16.9) for the neurologic patients, and 97.5 (4.4) for the control group (P < 0.001; study patients vs. controls). The MDADI was also sensitive to disease severity as measured by different food textures. The Swedish version of the MDADI showed good psychometric properties and is a valid instrument to assess dysphagia-related quality of life. It was also shown to be a reliable instrument after correction for systematic errors in the subjects' responses to two reversed questions. Its known-group validity enables the differentiation between dysphagic and nondysphagic patients for group-level research.