Organizational justice and insomnia: Relationships between justice components and insomnia symptoms among private company workers in Japan

Abstract

Objectives: Organizational justice (OJ) is an important psychosocial factor and it consists of several components. Previous studies have shown that low perceived OJ is associated with various health problems. However, the relationships between each justice component and health outcomes have not been fully examined. The purpose of this study was to clarify the relationships between OJ and insomnia, including OJ components and insomnia symptoms. Methods: Cross-sectional self-reported questionnaire data from 1,893 employees (92.2% of subjects) were collected. OJ was measured using the Japanese version of the OJ questionnaire, which has four components (distributive, procedural, interpersonal and informational). Insomnia was assessed with the Athens Insomnia Scale. Logistic regression analysis, with insomnia as a dependent variable and OJ as an independent variable, was conducted. Results: Subjects with low overall OJ had a higher risk of insomnia (adjusted odds ratio (AOR), 2.37; 95% confidence interval (CI), 1.59 to 3.53) and two insomnia symptoms (AOR of 2.47 and 95% CI of 1.68 to 3.65 for sleep induction problem; AOR of 1.73 and 95% CI of 1.21 to 2.48 for sleep maintenance problem). The four justice components were all associated with insomnia and sleep induction problems. Sleep maintenance problems were associated with only the distributive justice component. Conclusions: All four justice components were associated with both insomnia and sleep induction problems. Sleep maintenance problems, however, showed different features. Specifically, the distributive justice component seemed to be a key factor in the relationship between OJ and insomnia. These findings might provide useful information for preventing the adverse effects of insomnia.

(J Occup Health 2015; 57: 142–150)

Introduction

Organizational Justice (OJ) has been a notable psychosocial factor in the workplace for the past 10 years. Low perceived OJ is reported to be associated with a variety of health problems, such as self- rated poor health¹⁾, psychological distress^1–5), depression⁶⁾ and coronary heart disease⁷⁾. The concept of OJ consists of four components⁸⁾, the most acknowledged of which is distributive justice, an assessment of the fairness of outcome allocation⁹⁾. The second component is procedural justice, which is fairness derived in the process of decision evaluation^{10, 11)}. It has been reported that perceptions of procedural justice are often influenced by interactional elements, which can be seen as the other two dimensions of justice: interpersonal justice and informational justice. Interpersonal justice refers to respect and sensitivity aspects of interactional elements, which assesses the dignity and respect received from managerial authority. Informational justice, however, is an explanatory aspect of interactional elements, which assesses the degree of explanations from managerial authority^{12, 13)}.

Until recently, research on OJ has examined the unique effects of each justice perception separately on various outcomes. However, lately, research considering all justice components simultaneously has increased, as it might provide a more comprehensive understanding of justice¹⁴⁾. At this time, there are very few studies that have investigated the relationships among all four justice components and health problems.

Insomnia is one of the most common health problems worldwide¹⁵⁾. It can be related to a variety of physical and mental disorders, such as mood disorders, chronic pain, hypertension and diabetes mellitus¹⁶⁾. In addition, for workers, several studies have reported that insomnia is associated with a higher risk of work accidents, increased absenteeism, poorer performance, and less productivity^17–21). The social burden due to insomnia is large, and has serious consequences, especially in occupational settings.

Psychosocial work-related factors, including OJ, are important determinants of insomnia among working populations^22–27). A previous study revealed that low interactional justice is associated with insomnia among civil servants²⁷⁾. However, to our knowledge, no research has examined the relationships among insomnia and all justice components simultaneously, though it would help to understand the comprehensive effect of OJ on insomnia, and it may provide useful information in attenuating the impact of insomnia in the workplace.

Moreover, several insomnia symptoms such as difficulty with sleep induction and difficulty with maintaining sleep are rarely investigated separately. Each insomnia symptom may have its own determinants, while they may also share some of the same determinants. Therefore, examining the relationships between psychosocial work-related factors and each insomnia symptom would provide more useful and practical information. However, to date, little research has explored these relationships^{27, 28)}.

In this study, we investigated the relationships among all justice components and insomnia, and each insomnia symptom separately among workers at a private company.

Subjects and Methods

Subjects and procedure

A survey was conducted in June 2010, at an office of a manufacturing company. All full-time regular employees (N=2,058) were invited to participate in the survey, which was performed with a self-administered questionnaire. The questionnaire was designed to be anonymous to protect the privacy of the respondents. About 90% of the data were collected through the use of a security-protected intranet that the workers could connect to with their own computers, whereas the other 10% of the data were obtained by paper questionnaires collected in a sealed envelope.

A total of 1,893 employees participated in this survey, and the response rate was 92.2%. After excluding shift workers and participants under treatment for sleep disorders or mental disorders, 1,623 employees (78.9% of the original study sample) were included in the analysis. Written informed consent was not obtained beforehand. Nevertheless, the questionnaire was designed so that all the participants had to read the instructions and explanation for the survey before they started it, and responses were voluntarily requested. The study protocol was approved by a health information and research ethics committee at the company headquarters.

Measures

Organizational justice

Organizational justice was measured using the Japanese version of the OJ questionnaire, which has been reported to have high internal reliability and validity²⁹⁾; it is a translated version of the OJ questionnaire originally created and validated by Colquitt⁸⁾. It includes 20 items and four dimensional scales: distributive, procedural, interpersonal, and informational justice. All items were assessed using a 5-point Likert scale ranging from 1 to 5, and a high score represented high OJ.

Insomnia and sleeping hours

Insomnia was measured using the Athens Insomnia Scale.(AIS)^{30, 31)} We chose the AIS because it is based on ICD-10 criteria (nonorganic sleep disorder). It consists of eight items. The first five items assess difficulty with sleep induction, awakening during the night, early morning awakening, total sleep time, and overall sleep quality. The last three items assess the daytime consequences of insomnia (problems with sense of well-being, functioning, and sleepiness during the day). Each item was rated on a scale of 0 (no problem at all) to 3 (very serious problem), and the total AIS score ranges from 0 to 24. The respondents were requested to rate a sleep difficulty as positive if they had experienced it at least three times a week during the last month. In the AIS, the optimum cutoff score is set as 6 for individuals suspected of being insomniacs based on the sensitivity and specificity derived by comparison with the diagnosis of ICD-10 “nonorganic insomnia” by a medical interview³¹⁾.

The subjects were also asked about their average duration of sleep per night on weekdays. The choices were as follows: less than 4 hours per day, 4 to 5 hours per day, 5 to 6 hours per day, 6 to 7 hours per day, 7 to 8 hours per day, and more than 8 hours per day.

Job stress characteristics

Job stress characteristics were measured by the Brief Job Stress Questionnaire³²⁾. This scale was developed through research funded by a research grant from the Japanese Ministry of Labor with reference to Karasek's Job Content Questionnaire and the National Institute for Occupational Safety and Health Genetic Job Stress Questionnaire. Job demand was evaluated with a three-item quantitative job demand scale. Job control was evaluated with a three-item job control scale. Social support at work was evaluated with a three-item scale for coworker support and a three-item scale for supervisor support. All items were assessed using a 4-point Likert scale ranging from 1 to 4, and the total scores ranged from 3 to 12. A high score showed high job demand, high job control, and high social support, respectively.

Characteristics of the subjects

The questions asked were about: sex, age, marital status, type of occupation, working conditions (shift work, others), occupational status (manager, deputy manager, regular employee), overtime work hours per month (less than 20 hours, 20 to 45 hours, 45 to 80 hours, more than 80 hours), absence due to sickness during the previous year (none, less than 5 days, 5 to 10 days, more than 10 days), smoking status (current smokers vs nonsmokers), drinking frequency (never or occasionally vs almost every day), regular physical activity (more than half an hour of exercise is conducted two times or more per week), mental disorders (under medical treatment vs not), and sleep disorders (under medical treatment vs not).

Statistical Analysis

Firstly, we conducted correlation analyses between all the combinations of examined scales including OJ and job stress characteristics. Cronbach's α coefficient was calculated for all scales to confirm internal consistency reliability.

Logistic regression analysis

The association between OJ and insomnia was examined using logistic regression analysis. A test for trends and Hosmer and Lemeshow goodness-of-fit test were also conducted. Results are presented as odds ratios (ORs) and 95% confidence intervals (CIs) adjusted for sex, age, occupational status, overtime work, smoking status, drinking frequency, regular physical activity, job demand, job control, coworker support and supervisor support. The justice measures were divided into quartiles and treated as categorical variables. Overall OJ (summative scores of four justice components) and each justice component separately were examined. Subjects with insomnia were defined as those who had an AIS score of 6 or more^{30, 31)}. Furthermore, with each item of the insomnia symptoms, the scores were divided into two groups, “0” (absence of problem) and “1–3” (presence of problem). Participants displaying the presence of a problem were regarded as possessing that symptom. A sleep induction problem was defined as having difficulty with sleep induction. Those who experienced either awakening during the night or early morning awakening were classified as having a sleep maintenance problem. Statistical significance was set at p<0.05. All data were analyzed using SPSS Version 11.5J (SPSS, Japan Inc, Tokyo, Japan).

Results

Subject characteristics

The study subjects' characteristics are shown in Table 1. The majority of subjects were men (89.6%), in their forties (31.5%) who were engaged in engineering work (80.2%). The percentage of subjects working an extra 20 to 45 hours per month was 43.9%, and 45.2% of the subjects slept 5 to 6 hours per day. The prevalence of an insomnia score of 6 or more on the AIS was 29.8%. Of the subjects, 490 (30.2%) had a sleep induction problem, and 676 (41.7%) had a sleep maintenance problem.

Table 1. Characteristics of the subjects

Variables		n	%
Sex	Male	1,454	89.6
	Female	169	10.4
Age (years)	≤29	359	22.1
	30–39	486	29.9
	40–49	511	31.5
	50≤	267	16.5
Marital status	Married	954	58.8
	Other	669	41.2
Type of occupation	Technician	1,302	80.2
	Worker	39	2.4
	Manager	139	8.6
	Clerk	133	8.2
	Other	10	0.6
Occupational status	Managerial position	339	20.9
	Deputy manager	550	33.9
	Regular employee	734	45.2
Overtime work (hours/month)	<20	529	32.6
	≤20–45<	712	43.9
	≤45–80<	352	21.7
	80≤	30	1.8
Sleeping hours (hours/day)	<4	26	1.6
	≤4–5<	274	16.9
	≤5–6<	733	45.2
	≤6–7<	525	32.3
	≤7–8<	62	3.8
	8≤	3	0.2
Current smoker		370	22.8
Drinking frequency (almost every day)		431	26.6
Regularly physically active		429	26.4
Insomnia (Athens Insomnia Scale Score 6≤)		484	29.8
Sleep induction problem		490	30.2
Sleep maintenance problem		676	41.7

Scale characteristics and the results of correlation analysis

Table 2 shows descriptive characteristics and results of Spearman's correlation analysis of OJ and job stress characteristics. The Cronbach's α reliability coefficients were all in the preferable range (0.73 to 0.97).

Table 2. Descriptive statistics, reliability coefficients, and Spearman's rank correlation coefficients of organizational justice and job stress characteristics (n=1,623)

Variables (range)	Means	SD	Cronbach's α	1	2	3	4	5	6	7	8
1. Procedural justice (7–35)	24.5	5.9	0.93	1.000
2. Distributive justice (4–20)	14.4	3.7	0.97	0.735*	1.000
3. Interpersonal justice (4–20)	16.4	3.0	0.93	0.535*	0.499*	1.000
4. Informational justice (5–25)	18.8	4.4	0.93	0.736*	0.675*	0.711*	1.000
5. Overall organizational justice (20–100)	74.2	14.8	0.97	—	—	—	—	1.000
6. Job demand (3–12)	8.8	2.1	0.83	−0.052	−0.031	0.000	−0.052	−0.041	1.000
7. Job control (3–12)	8.2	1.8	0.73	0.252*	0.224*	0.235*	0.254*	0.277*	−0.257*	1.000
8. Supervisor support (3–12)	8.0	2.0	0.82	0.468*	0.422*	0.533*	0.600*	0.574*	0.039	0.312*	1.000
9. Coworker support (3–12)	8.3	1.9	0.82	0.389*	0.358*	0.410*	0.452*	0.454*	0.014	0.258*	0.695*

*  p<0.05.

Results of logistic regression analysis

The results of the logistic regression analysis showed that low OJ (overall OJ and each justice component) was significantly associated with a higher risk of insomnia. All the results of the test for trends were also all significant. Even after adjustment for sex, age, occupational status, overtime work, smoking status, drinking frequency, regular physical activity, job demand, job control, coworker support and supervisor support, these associations remained significant (Table 3).

Table 3. Odds ratios of insomnia^† by levels of organizational justice (n=1,623)

Overall organizational justice (quartiles)	Range	N (%)	Unadjusted OR (95% CI)	p	Adjusted OR (95% CI)※‡	p
1 (low)	20–65	410 (25.3)	3.32 (2.41–4.59)	<0.001	2.37 (1.59–3.53)	<0.001
2	66–76	415 (25.6)	1.93 (1.39–2.68)	<0.001	1.65 (1.15–2.38)	0.007
3	77–83	411 (25.3)	1.56 (1.11–2.19)	0.010	1.44 (1.00–2.06)	0.048
4 (high)	84–100	387 (23.8)	1.00		1.00
Test for trend			p<0.001		p<0.001
Procedural justice (quartiles)			Unadjusted OR (95% CI)	p	Adjusted OR (95% CI)※‡	p
1 (low)	7–20	305 (18.8)	2.85 (1.99–4.09)	<0.001	1.82 (1.20–2.77)	0.005
2	21–24	444 (27.4)	2.10 (1.49–2.96)	<0.001	1.64 (1.13–2.38)	0.010
3	25–28	559 (34.4)	1.53 (1.09–2.14)	0.038	1.37 (0.96–1.95)	0.084
4 (high)	29–35	315 (19.4)	1.00		1.00
Test for trend			p<0.001		p=0.004
Distributive justice (quartiles)			Unadjusted OR (95% CI)	p	Adjusted OR (95% CI)※‡	p
1 (low)	4–11	249 (15.3)	3.29 (2.23–4.85)	<0.001	2.28 (1.46–3.55)	<0.001
2	12–15	488 (30.1)	2.44 (1.71–3.46)	<0.001	1.98 (1.36–2.91)	<0.001
3	16	598 (36.8)	1.51 (1.06–2.15)	0.021	1.40 (0.96–2.02)	0.079
4 (high)	17–20	288 (17.7)	1.00		1.00
Test for trend			p<0.001		p<0.001
Interpersonal justice (quartiles)			Unadjusted OR (95% CI)	p	Adjusted OR (95% CI)※‡	p
1 (low)	4–15	448 (27.6)	2.75 (2.03–3.74)	<0.001	2.04 (1.41–2.93)	<0.001
2	16	513 (31.6)	1.51 (1.11–2.06)	0.008	1.34 (0.96–1.87)	0.085
3	17–19	257 (15.8)	1.48 (1.03–2.13)	0.035	1.34 (0.91–1.96)	0.137
4 (high)	20	405 (25.0)	1.00		1.00
Test for trend			p<0.001		p<0.001
Informational justice (quartiles)			Unadjusted OR (95% CI)	p	Adjusted OR (95% CI)※‡	p
1 (low)	5–16	432 (26.6)	2.41 (1.80–3.22)	<0.001	1.56 (1.08–2.26)	0.018
2	17–19	328 (20.2)	1.40 (1.01–1.93)	0.043	1.10 (0.77–1.57)	0.600
3	20	408 (25.1)	1.15 (0.84–1.58)	0.367	0.99 (0.71–1.38)	0.946
4 (high)	21–25	455 (28.0)	1.00		1.00
Test for trend			p<0.001		p=0.012

^†  Insomnia is indicated by an AIS (Athens Insomnia Scale) score of 6 or higher. There were 484 (29.8%) participants with insomnia in this study.

^※  Adjusted for sex, age, occupational status, overtime work, smoking status, drinking frequency, regular physical activity, job demand, job control and coworker support.

^‡  Hosmer and Lemeshow goodness-of-fit test revealed adequate model fit (p>0.05).

Among the relationships between OJ and sleep symptoms, overall OJ was associated with both sleep induction problems and sleep maintenance problems. Even after adjustment for lifestyle and work-related variables, these associations remained significant. Procedural justice, distributive justice, interpersonal justice, and informational justice were all associated with increased risk of sleep induction problems. Among the four components, only distributive justice was associated with sleep maintenance problems (Table 4).

Table 4. Odds ratios of insomnia symptoms^† by levels of organizational justice (n=1,623)

			sleep induction problem	n (%) 490 (30.2)	sleep maintenance problem	n (%) 676 (41.7)
Overall organizational justice (quartiles)	Range	N (%)	Adjusted OR (95% CI)※‡	p	Adjusted OR (95% CI)※‡	p
1 (low)	20–65	410 (25.3)	2.47 (1.68–3.65)	<0.001	1.73 (1.21–2.48)	0.030
2	66–76	415 (25.6)	1.61 (1.13–2.30)	0.009	1.17 (0.85–1.61)	0.341
3	77–83	411 (25.3)	1.55 (1.10–2.19)	0.013	1.39 (1.02–1.89)	0.038
4 (high)	84–100	387 (23.8)	1.00		1.00
Test for trend			p<0.001		p=0.015
Procedural justice (quartiles)			Adjusted OR (95% CI)※‡	p	Adjusted OR (95% CI)※‡	p
1 (low)	7–20	305 (18.8)	2.06 (1.37–3.11)	0.001	1.44 (0.99–2.09)	0.058
2	21–24	444 (27.4)	1.78 (1.23–2.56)	0.002	1.35 (0.97–1.88)	0.071
3	25–28	559 (34.4)	1.55 (1.09–2.19)	0.014	1.07 (0.79–1.46)	0.668
4 (high)	29–35	315 (19.4)	1.00		1.00
Test for trend			p<0.001		p=0.018
Distributive justice (quartiles)			Adjusted OR (95% CI)※‡	p	Adjusted OR (95% CI)※‡	p
1 (low)	4–11	249 (15.3)	2.52 (1.62–3.94)	<0.001	2.21 (1.48–3.30)	<0.001
2	12–15	488 (30.1)	2.42 (1.65–3.54)	<0.001	1.36 (0.97–1.90)	0.072
3	16	598 (36.8)	1.74 (1.20–2.52)	0.003	1.24 (0.91–1.70)	0.178
4 (high)	17–20	288 (17.7)	1.00		1.00
Test for trend			p<0.001		p<0.001
Interpersonal justice (quartiles)			Adjusted OR (95% CI)※‡	p	Adjusted OR (95% CI)※‡	p
1 (low)	4–15	448 (27.6)	1.78 (1.25–2.54)	0.001	1.08 (0.78–1.50)	0.648
2	16	513 (31.6)	1.35 (0.98–1.85)	0.067	1.09 (0.82–1.46)	0.558
3	17–19	257 (15.8)	0.98 (0.67–1.44)	0.935	1.04 (0.74–1.46)	0.812
4 (high)	20	405 (25.0)	1.00		1.00
Test for trend			p<0.001		p=0.598
Informational justice (quartiles)			Adjusted OR (95% CI)※‡		Adjusted OR (95% CI)※‡
1 (low)	5–16	432 (26.6)	1.49 (1.04–2.14)	0.031	1.07 (0.78–1.50)	0.701
2	17–19	328 (20.2)	1.30 (0.92–1.83)	0.141	0.94 (0.69–1.30)	0.715
3	20	408 (25.1)	1.15 (0.83–1.59)	0.410	0.96 (0.71–1.28)	0.759
4 (high)	21–25	455 (28.0)	1.00		1.00
Test for trend			p=0.024		p=0.720

^†  Participants who had experienced sleep difficulties at least three times a week during the last month.

^※  Adjusted for sex, age, occupational status, overtime work, smoking status, drinking frequency, regular physical activity, job demand, job control and coworker support.

^‡  Hosmer and Lemeshow goodness-of-fit test revealed adequate model fit (p>0.05).

Discussion

Our results showed that workers at a private company with low overall OJ had a higher prevalence of insomnia. In addition, we examined each justice component separately, and observed that all justice components, distributive justice, procedural justice, interpersonal justice and informational justice, were related to insomnia in a dose-response manner.

The results showed that the distributive justice component was the strongest factor related to insomnia among the four components, and its OR was almost equal to that of overall OJ. This result was as expected because distributive justice shares a common underlying theory with the Effort-Reward Imbalance (ERI) Model. The ERI Model is one of the well-established occupational stress models. It focuses on the reciprocity of exchange in occupational life, and high-effort/low-reward conditions are considered stressful³³⁾. Previous research showed that ERI is a risk factor of insomnia in workers^23–25). Both distributive justice and ERI measure the ratio between input and output, and it has been pointed out that distributive justice focuses on interpersonal comparisons, while ERI is based primarily on intrapersonal comparisons^{34, 35)}.

The OR of the interpersonal justice component was the second highest. A previous study showed that interactional justice (interpersonal justice and informational justice were not separated) is associated with insomnia among civil servants. The present study shows that interpersonal justice is also associated with insomnia among private company workers, and this result suggests that relationships between interactional justice and insomnia are consistent across different occupational settings. There has been only one intervention study that has proved supervisory training in interpersonal justice is effective for attenuating insomnia symptoms among hospital staff³⁶⁾. Accordingly, in another occupational setting, such as the private company in this study, a program to train management in interpersonal justice might be an effective intervention to prevent insomnia in staff.

Although a previous study found that low interactional justice (interpersonal justice and informational justice were not separated) is associated with insomnia among civil servants²⁷⁾, this is the first study to reveal that each justice component has a different impact on insomnia. Furthermore, this study revealed that both interpersonal justice and informational justice had adverse effects on insomnia, and the OR of interpersonal justice was higher compared with that of informational justice. This result suggests that a supervisor's attitude with regard to fairness should be a higher priority in considering the relationships between OJ and insomnia.

Another finding revealed in this study was the significant associations among OJ and insomnia symptoms. We assessed insomnia symptoms based on AIS items. Of the subjects, 490 (prevalence 30.2%) had a sleep induction problem. Those who experienced either awakening during the night (prevalence 23.9%) or early morning awakening (prevalence 35.6%) were classified as having a sleep maintenance problem (prevalence 41.7%). The prevalence of insomnia symptoms, especially sleep maintenance problems, seemed to be high. Because we defined the possession of insomnia symptoms based on AIS items, regardless of insomnia severity, we cannot rule out the possibility of overestimation. It is possible that subjects who had insomnia symptoms with no clinical significance were included. However, in comparison with the previous studies conducted in Japanese populations^{37, 38)}, the prevalence of insomnia symptoms in this study was in a similar range. Thus, we have retained this definition.

Both sleep induction problems and sleep maintenance problems were associated with overall OJ. Sleep induction problems were also associated with all four justice components. In contrast, sleep maintenance problems showed different features. Only the distributive justice component was associated with. In addition, the procedural justice component company employees) should be considered. Further ous occupational settings is needed to examine these relationships. According to a previous study, high whereas there is no significant association with sleep maintenance problems showed marginal significance, whereas the trend was statistically significant. A previous longitudinal study of civil servants showed that an interactional justice component is associated with increased risk of both sleep induction problems and sleep maintenance problems in men²⁷⁾. However, the results of this study showed that there was no relationship between interactional justice (interpersonal justice and informational justice) and sleep maintenance problems. These differences may be explained by several factors. The prevalence of insomnia symptoms has been found to rise with age, and its pattern of increase was characterized by sex and occupational class³⁹⁾. In relation to this, the effects of OJ on insomnia symptoms may have been overestimated, since a previous study had ten years' lag time between exposure and outcome. In addition, the differences in the subjects' characteristics (i.e., male-female ratio, civil servants or company employees) should be considered. Further research with a shorter observation period and in various occupational settings is needed to examine these relationships. According to a previous study, high job strain is associated with sleep induction problems, whereas there is no significant association with sleep maintenance problems²⁸⁾. We conducted an additional logistic regression analysis to reveal the relationships between high job strain and insomnia symptoms in this study's data set. The results showed that high job strain was associated with sleep induction problems, whereas there was no significant association with sleep maintenance problems. After adjusting for covariates and overall OJ, these relationships remained consistent (data not shown). In consideration of our research results and previous research findings, we suggest that psychosocial work-related factors, such as job strain and OJ, might have a notable influence on sleep induction problems.

In discussion of workers' sleep problems, we have to consider working hours, since hours that could have been spent sleeping are often spent working. In comparison with a previous cross-sectional study on insomnia in a Japanese occupational setting³⁸⁾, our subjects had longer working hours (67.4% of our subjects worked more than 20 extra hours per month, meanwhile, 39.4% of the previous study's subjects worked more than 45 hours per week, which is almost equal to working an extra 20 hours per month). Therefore, there is a possibility that long working hours forced our subjects into a higher sleep debt. Generally, the sleep debt population tends to fall asleep easily. However, our subjects also had a higher rate of sleep induction problems (30.2% of our subjects versus 24.8% of the previous study's subjects). It is suggested that longer working hours are theoretically related to short sleep duration, but at the same time, it might be a result of unfavorable psychosocial work-related factors, such as organizational injustice, which might cause difficulty initiating sleep.

The distributive justice component showed a notable effect on both insomnia symptoms, and the OR was higher than that of overall OJ. Consequently, focusing on the distributive justice component would help us to distinguish which workers suffer from insomnia arising from psychosocial work stress.

Several study limitations need to be discussed. First, this study was a cross-sectional study, and causal relationships could not be examined. A previous study showed that there might be reciprocal relationships between psychosocial work-related factors and sleep disorders²⁶⁾; however, some longitudinal studies are needed. Second, all survey items were self-reported, and not measured objectively. For instance, obtaining ratings of OJ from supervisors or colleagues may be preferable⁴⁰⁾. Nevertheless, we could not use these sources in our study, because it was conducted anonymously with regard to the person as well as the department. Third, the present study sample consisted of regular employees of a large private company, mainly white-collar men, and the results cannot be generalized to other types of workers such as temporary workers, women and blue-collar workers. As an example, the effect of OJ on psychological distress might be different according to gender and employment status⁴¹⁾. More studies in different organizational settings would be beneficial. These limitations aside, this study had a high response rate and significantly, it found showed that all four justice components are related to both insomnia and insomnia symptoms. The results of this study suggest that improvement of psychosocial factors in the workplace and pharmacological treatment and non-pharmacological treatment approaches, such as cognitive behavioral therapy⁴²⁾, could be important countermeasures against insomnia in workers.

In conclusion, this study showed that workers with low perceived OJ with regard to all four justice components were associated with insomnia and sleep induction problems. Sleep maintenance problems had different features. The distributive justice component might be a major factor in the relationship between OJ and insomnia. It is also suggested that sleep induction problems could be the most significant insomnia symptom caused by psychosocial work-related factors. These findings may provide useful information for preventing the adverse effects of insomnia in occupational settings.

References

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