Reliability and validity of the Japanese version of the Sleep Problem Acceptance Questionnaire

This study aimed to develop a Japanese version of the Sleep Problem Acceptance Questionnaire (SPAQ-J) and assess its reliability and validity. The SPAQ-J was developed through a forward-backward translation procedure with permission from the original authors. The sample included 861 adults with insomnia who completed questionnaires on experiential avoidance, insomnia symptoms, dysfunctional beliefs about sleep, sleep-related safety behaviors, insomnia catastrophizing, and pre-sleep arousal. Confirmatory factor analysis confirmed that the SPAQ-J retained the two-factor structure of the original version (CFI = 0.972, TLI = 0.958, RMSEA = 0.082, SRMR = 0.059): Activity Engagement and Willingness. Although internal consistency was adequate (Activity Engagement: α = 0.868, ω = 0.870; Willingness: α = 0.895, ω = 0.895), test-retest reliability was below the recommended threshold (Activity Engagement: ICC = 0.586, Willingness: ICC = 0.589). In terms of construct validity, Willingness moderately correlated with all scales, whereas Activity Engagement showed moderate-to-weak correlations. Hierarchical multiple regression analysis revealed that adding the SPAQ-J subscales significantly enhanced the explanatory power. Measurement invariance analysis across sex and age groups showed no significant changes in the fit indices, indicating stability. These findings suggest that the SPAQ-J is a valid and partially reliable measure of psychological flexibility related to sleep problems in the Japanese population.