Abstract
PurposePatient-reported outcome measures are essential in the evaluation of facial palsy. Aim of this study was to translate and validate the Facial Disability Index (FDI) for use in the Netherlands.MethodsThe FDI was translated into Dutch according to a forward-backward method. Construct validity was assessed by formulating 22 hypotheses regarding associations of FDI scores with the Facial Clinimetric Evaluation scale, the Synkinesis Assessment Questionnaire, the Short Form-12 and the Sunnybrook Facial Grading System. Validity was considered adequate if at least 75% (i.e. 17 out of 22) of the hypotheses were confirmed. Additionally, confirmatory factor analysis was performed. Cronbach’s α was calculated as a measure of internal consistency. Participants were asked to fill out the FDI a second time after 2 weeks to analyse test-retest reliability. Lastly, smallest detectable change was calculated.ResultsIn total, 19 hypotheses (86.4%) were confirmed. Confirmatory factor analysis showed acceptable fit for the two factor structure of the original FDI (root mean square error of approximation = 0.064, standardized root mean square residual = 0.081, comparative fit index = 0.925, Chi-square = 50.22 with 34 degrees of freedom). Internal consistency for the FDI physical function scale was good (α > 0.720). Internal consistency for the FDI social/well-being scale was slightly less (α > 0.574). Test-retest reliability for both scales was good (intraclass correlation coefficients > 0.786). Smallest detectable change at the level of the individual was 17.6 points for the physical function and 17.7 points for the social/well-being function, and at group level 1.9 points for both scales.ConclusionThe Dutch version FDI shows good psychometric properties. The relatively large values for individual smallest detectable change may limit clinical use. The translation and widespread use of the FDI in multiple languages can help to compare treatment results internationally.
Highlights
Facial palsy results in functional and social problems related to the inability to control the muscles of facial expression [1,2,3,4]
No problems in the wording and phrasing of the consensus version Facial Disability Index (FDI)-NL were identified during pilot testing
Confirmatory factor analysis examining the fit of the original two latent factors of the FDI showed an acceptable level of fit for the Dutch version FDI with a root mean square error of approximation of 0.064, standardized root mean square residual of 0.081, comparative fit index of 0.925, and Chi-square value of 50.22 with 34 degrees of freedom [23,24,25,26]
Summary
Facial palsy results in functional and social problems related to the inability to control the muscles of facial expression [1,2,3,4]. The altered facial function and appearance of the face may increase feelings of depression and anxiety, and may negatively influence selfimage and quality of life [3,4,5,6,7]. The latter describes not so much the condition affecting the individual, but rather the individuals perception on their position in life including their social environment and mental health in the context of the condition. Aim of this study was to translate the FDI into Dutch and culturally validate the Dutch version of the FDI (FDI-NL) for use in Dutch speaking populations
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