Psychometric properties of the mutuality scale in Swedish dyads with Parkinson's disease

The 15-item mutuality scale (MS) has been used in several neurological conditions assessing the quality of relationship associations with negative effects of the caregiving situation. The aim of this study was to translate the original MS into Swedish and assess its psychometric properties in Parkinson's disease (PD).

Following the forward-backward translation method, the scale was evaluated regarding linguistic correctness at a conceptual level and user-friendliness. The scale was filled out by a sample of 50 care dyads where one was having PD. Scale assumptions and scale structure were evaluated using floor/ceiling effect and principal component analyses (PCA) with promax rotation. Internal consistency was evaluated using Cronbach's alpha and mean inter-item correlation coefficients.

The Swedish MS was evaluated as user-friendly and relevant by the participants. The scale demonstrated no floor/ceiling effect and showed high internal consistency (α≥0.93) with a mean inter-item correlation coefficient of ≥0.5. Through the PCA, a two factor solution emerged, which accounted for 67% and 64% of the variance of the MS score by PD-partners and PD-patients, respectively. However, some variables were complex and discarded in the final solution.

Our findings provide initial support of the Swedish MS as a user-friendly and useful instrument with acceptable psychometric properties even though more research is needed to evaluate the existence of subscales.