Development of Japanese version of the checklist individual strength questionnaire in a working population.

The aims of the present study were to develop and validate the Japanese version of the checklist individual strength questionnaire (CIS) which is used to measure prolonged fatigue not only in the general population but also in the working population. We obtained permission to use CIS from its author and translated the questionnaire into Japanese. Then, the Japanese version of the questionnaire was translated back into English by a bilingual person. The author of the original version agreed that the back-translated version was conceptually and linguistically equivalent to the original CIS. To validate CIS, 399 workers (66.7% were men) from different companies answered the Japanese version of the CIS (CIS-J), Maslach burnout inventory-general survey (MBI-GS), Beck Depression Inventory-II (BDI-II), visual analogue scale (VAS) questionnaires for subjective fatigue, number of overtime hours and number of hours of sleep. Cronbach's α for the total CIS-J score was 0.91. The test-retest reliability assessed with an intra-class correlation coefficient was 0.82. Although confirmatory factor analysis did not show an ideal model fit, the correlation coefficients between the total CIS score and the MBI-GS exhaustion score, the BDI-II score and the VAS score were 0.58 (p<0.01), 0.66 (p<0.01) and 0.63 (p<0.01), respectively. The less workers slept and the longer they worked, the higher their total CIS score became. CIS-J showed good reliability and acceptable validity in the working population. Thus, it could be useful for studying fatigue among Japanese working populations.