How Valid and Reliable Is the International Dysphagia Diet Standardisation Initiative (IDDSI) When Translated into Another Language?

Swallowing difficulties are estimated to affect 590 million people worldwide and the modification of food and fluids is considered the cornerstone of dysphagia management. Contemporary practice uses the International Dysphagia Diet Standardisation Initiative (IDDSI), however, the validity and reliability of IDDSI when translated into another language has not been investigated. This study describes the translation process and confirms the validity and reliability of IDDSI when translated into another language (Swedish). The translation used a 12-step process based on the World Health Organization recommendations. Validity was tested using Content Validity Index (CVI) based on three ratings by a panel of 10-12 experts (Dietitians and Speech-Language Pathologists [SLPs]). The translation was rated for linguistic correlation as well as understandability and applicability in a Swedish context. Inter-rater reliability was calculated using Intraclass Correlation Coefficient (ICC) from 20 SLP assessments of 10 previously published patient cases. Significant improvement (p < 0.05) of CVI between Expert Panel assessments was shown for linguistic correlation (improvement from 0.74-0.98) and understandability/applicability (improvement from 0.79-0.93 across ratings). Excellent validity (Item-CVI > 0.78 and Scale-CVI/Average > 0.8) and very high inter-rater reliability (ICC > 0.9) were demonstrated. Results show that, when using a multi-step translation process, a translated version of IDDSI (into Swedish) demonstrates high validity and reliability. This further contributes to the evidence for use of IDDSI.