Exploratory factor analysis of the Modified Somatic Perception Questionnaire on a sample with insomnia symptoms.

OBJECTIVES The purpose of this study was to examine the factorial solution of the Modified Somatic Perception Questionnaire (MSPQ) among individuals with insomnia symptoms in the general population. DESIGN A cross-sectional study with a randomly selected sample from the general population (N = 3600; 20-60 year old) was used. In total, 251 of the 2179 respondents fulfilled the criteria for insomnia symptoms and filled out a survey on demographic parameters, the MSPQ, the Hospital Anxiety and Depression Scale, sleep medication use and health care consumption. METHODS Exploratory factor analysis and correlations were used. RESULTS The results showed that a two-factor solution, accounting for 47.31% of the variance, was extracted from the 13 items of the MSPQ. Although one factor consisting of 10 items determined general symptoms of somatic arousal (alpha = 0.83), the other factor with three items assessed stomach symptoms and nausea (alpha = 0.78). The two factors were significantly inter-correlated (r = 0.54) and significantly associated with the total MSPQ (r = 0.96, r = 0.74). The two factors also showed discriminant validity with anxiety and depression and predictive validity with retrospective reports of sleep medication use and health care consumption. A few significant interactions emerged the two MSPQ factors and degree of sleep complaints. CONCLUSIONS Although it is often assumed that the MSPQ taps a single factor of somatic arousal, this study on individuals with insomnia symptoms suggests that a two-factor solution has the best fit. Further research on the factorial solution of the MSPQ is warranted.