# Verification of sleep scales as predictors of suicidal ideation in Japanese dayworkers: a longitudinal study

## TL;DR

This study found that sleep quality measured by a specific scale can predict suicidal thoughts in Japanese workers over time.

## Contribution

The study demonstrates that the 3DSS sleep scale, but not the PSQI, predicts suicidal ideation in workers after adjusting for depression.

## Key findings

- 22 out of 293 participants developed suicidal ideation during the study period.
- Only the 3DSS sleep quality subscale significantly predicted suicidal ideation after adjusting for depressive symptoms.
- The PSQI did not show a significant predictive ability for suicidal ideation.

## Abstract

The objective of this study was to verify whether the assessment of poor sleep based on two sleep scales could predict suicidal ideation in Japanese dayworkers. A longitudinal survey was conducted among 446 Japanese dayworkers working at a company in Japan. Questionnaires were administered in 2013 (baseline) and 2014 (follow-up). To evaluate suicidal ideation, we used Question 19 of the Self-rating Depression Scale, categorizing participants who chose response options “some/a good part/most of the time” as suicidal ideation (+), and those who chose option “never or only a little of the time” as suicidal ideation (−). Two sleep scales, the Pittsburgh Sleep Quality Index (PSQI) and the 3-Dimensional Sleep Scale (3DSS), were selected as potential predictors of suicidal ideation. Only participants who were suicidal ideation (−) at baseline were included in the analysis, and suicidal ideation (+) individuals at follow-up were considered to have developed suicidal ideation during the interval between baseline and follow-up surveys. Data from 293 participants (236 men, 57 women) were analyzed. Twenty-two participants (7.5%) became suicidal ideation (+) at follow-up. Multiple logistic regression analysis showed that only sleep quality of the 3DSS subscale significantly predicted suicidal ideation, even after adjusting for depressive symptoms. That is, assessment of poor sleep did not predict suicidal ideation when based on the PSQI, but did when based on the 3DSS. Assessment of sleep quality based on the 3DSS may prove more useful in predicting worker suicidal ideation in industrial settings with limited facilities than PSQI.

The online version contains supplementary material available at 10.1007/s41105-022-00404-6.