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    Rights statement: This is the peer reviewed version of the following article: Maltby, J., Dale, M., Underwood, M., Simpson, J. and the REGISTRY investigators of the European Huntington's Disease Network (2017), Irritability in Huntington's Disease: Factor Analysis of Snaith's Irritability Scale. Mov Disord Clin Pract, 4: 342–348. doi:10.1002/mdc3.12424 which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/mdc3.12424/abstract This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.

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Irritability in Huntington’s Disease: factor analysis of Snaith’s Irritability scale

Research output: Contribution to journalJournal article

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<mark>Journal publication date</mark>05/2017
<mark>Journal</mark>Movement Disorders
Issue number3
Volume4
Number of pages7
Pages (from-to)342-348
Publication statusPublished
Early online date1/10/16
Original languageEnglish

Abstract

Background

Elevated levels of irritability are reported to occur in a number of neurological conditions, including Huntington's disease (HD), a genetic neurodegenerative disorder. Snaith's Irritability Scale (SIS) is used within HD research, but no psychometric evaluation of this instrument has previously been undertaken. Therefore, the current study aimed to analyze the factor structure of this scale among an HD population.

Methods

Exploratory and confirmatory factor analysis were used to examine the structural properties of SIS using responses from 1,264 HD gene expansion carriers, across 15 European countries, who were engaged in the REGISTRY 3 study.

Results

An exploratory factor analysis of a subsample of the data suggested a two-factor interpretation of the data comprising “temper” and “self-harm.” Eight possible models were tested for goodness of fit using confirmatory factor analysis. Two bifactor models, testing general and group factors in the structure of the scale, provided an equivocal “good” fit to the data. The first comprised a general irritability factor and two group factors (as originally proposed using SIS): outward irritability and inward irritability. The second comprised a general irritability factor and two group factors (as proposed by the exploratory factor analysis): temper and self-harm. The findings from both models suggested that the loadings of items were higher on the general factor.

Conclusions

Bifactor models are proposed to best consider the structure of the SIS, with findings suggesting that an overall score should be used to measure irritability within HD populations.

Bibliographic note

This is the peer reviewed version of the following article: Maltby, J., Dale, M., Underwood, M., Simpson, J. and the REGISTRY investigators of the European Huntington's Disease Network (2017), Irritability in Huntington's Disease: Factor Analysis of Snaith's Irritability Scale. Mov Disord Clin Pract, 4: 342–348. doi:10.1002/mdc3.12424 which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/mdc3.12424/abstract This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.