The effect of work-related and socio-demographic factors on Work Ability Index (WAI) among Iranian workers

Abstract

BACKGROUND:

The Work Ability Index (WAI) is a suitable and valid instrument, which provides a general view of workers’ abilities and functional capacities.

OBJECTIVE:

This study aimed to evaluate the effect of work-related and sociodemographic factors on work ability among employees of a company in Iran.

METHODS:

This cross-sectional study was conducted on 167 employees. Work ability was measured by the Persian version of WAI. A questionnaire was also developed to assess work-related and sociodemographic factors. The data were analyzed using univariate analysis of variance (ANOVA), independent t-test, and Pearson’s correlation.

RESULTS:

The mean (SD) score of WAI was 38.4 (6.4). WAI mean score (p < 0.05) was associated with age, gender, sleep quality, smoking, work schedule, the conflict between the work and individual, family, and social lives, work injuries, and job satisfaction.

CONCLUSIONS:

To improve the workers’ work ability, interventional programs should be concentrated on changing work schedules, improving sleep quality, limiting work hours, and not scheduling sensitive individuals to night shifts, those whose circadian rhythm stability and circadian rhythm amplitude is rigid type and languid type, respectively.

Keywords

Workplace stress sleep shift work schedule occupational health aging workforce

1 Introduction

Aging workforce is one of the basic problems that most organizations are currently encountering [1 –3]. Due to the increased susceptibility of illness and disease as individuals age, elderly individuals’ work ability constrains their health and quality of life [4].

Workforce populations in Iran, like many other developing countries, are aging rapidly [2, 3]. As a result, maintaining health and increasing working life (the part of a person’s life when they do a job or are at work) should be considered as a basic priority. One of the comprehensive solutions for achieving this goal is to maintain and promote work ability. In recent years, promoting work ability has been considered as one of the effective methods to prevent disability and reduce early retirement [5 –8].

The Finnish Institute of Occupational Health (FIOH) is one of the organizations, which expanded research in the field of work ability and workforce health. This institute designed and developed the Work Ability Index (WAI) in order to evaluate the work ability of the workforce [5 , 8]. Based on this index, the work ability concept assesses the workers’ role health at present and in the future according to their physical and mental abilities and occupational identities [2 , 9]. Nowadays, WAI is used as an international index and criterion for obtaining the ideal work ability. It is a suitable instrument used to create a general overview of functional capacity, work ability, and the factors associated with workability. Using this index, the personnel’s work ability problems can be determined, thus preventing or providing suitable initiatives and programs at the individual or organizational levels [3, 10]. The effectiveness of corrective initiatives can also be evaluated using this index. Eskelinen et al. showed that individual evaluation using the WAI was related well to clinical examinations [11]. This questionnaire has been also used in occupational health clinics and research in order to evaluate personal health, work environments, and early retirement [5 , 8].

Most of the studies in the field of WAI and its influential factors were performed in industrial and developed countries, but little information is available about developing countries, especially Iran. Moreover, the previous studies indicated that many work-related and sociodemographic factors influenced work ability [2 , 12]. However, the impacts of other work-related variables, such as occupational training, job satisfaction, having a second job, and conflict between work and individual, family, and social lives on WAI have been studied less often. Therefore, the present study aims to evaluate the WAI and the effects of sociodemographic and work-related factors among the personnel of an industrial company located in Iran.

2 Methods

2.1 Research design and studied population

The current cross-sectional study was performed in a cosmetic factory consisting of 190 workers in Yasuj, Iran in 2017. All workers were invited to participate in the study. At first, the researchers described the research goals for all company workers and after obtaining informed consents, the questionnaires were completed privately to maintain confidentiality. It should be noted that anonymous questionnaires were used and data were summarized. Totally, 167 personnel were willing to participate in this study (response rate: 88%). The ethical standards of the study were approved by the scientific and ethics committee of Yasuj University of Medical Sciences.

2.2 Instruments

2.2.1 Work Ability Index

In order to evaluate work ability, the Persian version of WAI was used. This index was originally developed by FIOH and contained seven dimensions (Table 1) [5, 8]. The score of the index was computed by summing the scores across the seven dimensions. Thus, the highest and lowest possible scores were 49 and 7, respectively. Finally, based on the obtained scores, work ability was classified into four categories, namely poor (7–27), moderate (28–36), good (37–43), and excellent (44–49). The WAI was translated into Persian and its validity and reliability were confirmed by Abdolalizadeh et al. in Iran [13].

Table 1
The relationships between the dimensions and final scores of WAI

WAI dimensions Mean Standard deviation ^*Correlation coefficient P

1. Current work ability compared to the lifetime best 8.1 1.8 0.66 0.000

2. Work ability in relation to the demands of the job 7.78 1.5 0.60 0.000

3. Number of current diseases diagnosed by a Physician 4.57 2.4 0.59 0.000

4. Estimated work impairment due to diseases 4.87 1.38 0.65 0.000

5. Sick leave during the past year 4.68 0.82 0.46 0.000

6. Own prognosis of work ability two years from now 5.83 1.89 0.64 0.000

7. Mental resources 5.38 0.89 0.45 0.000

WAI dimensions	Mean	Standard deviation	^*Correlation coefficient
1. Current work ability compared to the lifetime best	8.1	1.8	0.66
2. Work ability in relation to the demands of the job	7.78	1.5	0.60
3. Number of current diseases diagnosed by a Physician	4.57	2.4	0.59
4. Estimated work impairment due to diseases	4.87	1.38	0.65
5. Sick leave during the past year	4.68	0.82	0.46
6. Own prognosis of work ability two years from now	5.83	1.89	0.64
7. Mental resources	5.38	0.89	0.45

^*Pearson’s coefficient.

2.2.2 Work-related and sociodemographic factors

A questionnaire designed by Mokarami et al. was used in order to evaluate work-related and sociodemographic factors [3, 14]. These factors included age, gender, marital state, education level, smoking, exercise activity, sleep quality, job tenure, work schedule, second job, weekly hours, work nature, work load, conflicts between the work and individual, social, and family lives, work-related injuries, job training, and job satisfaction (it was measured with one question: “All in all, I am satisfied with my job”).

2.3 Statistical methods

The collected data were analyzed using the SPSS software, version 21 (USA, SPSS Inc.). Descriptive statistics were used for the characteristics of the study population. In order to evaluate the relationship between the dimensions and the final scores of WAI, Pearson’s correlation coefficients were used. Independent t-test and univariate analysis of variance (ANOVA) were used to examine the relationship between work-related and sociodemographic factors and the WAI score. A significance level was set at p < 0.05.

3 Results

Among the 167 studied workers, 89.9% were male and 10.1% were female. The mean (SD) age of the participants was 31.9 (5.1) years. Additionally, their means (SD) of job tenure and work hours were 5.1 (2.4) years and 58.5 (11.6) hours, respectively. The participants’ sociodemographic characteristics have been presented in Table 2.

Table 2
The participants’ sociodemographic features and their relationships with WAI meanscore (n = 167)

Characteristics n (%) Mean (SD) score of WAI P

Age group (years)

≤29 49 (29.3) 36.3 (7.5) 0.019^†

30–39 104 (62.3) 39.4 (5.6)

≥40 14 (8.4) 38.7 (7.0)

Gender

Male 150 (89.9) 38.0 (6.5) 0.004^‡

Female 17 (10.1) 42.1 (4.7)

Marital status

Single 26 (15.6) 38.4 (5.9) 0.968^‡

Married 141 (84.4) 38.4 (6.6)

Education level

Under diploma 21 (12.6) 37.0 (5.0) 0.453^†

Diploma 98 (58.7) 38.1 (6.9)

AD 16 (9.6) 39.2 (4.5)

BSc 29 (17.4) 39.6 (6.7)

Master’s and higher degrees 3 (1.8) 42.7 (4.2)

Sleep quality

Very good 8 (4.8) 43.9 (3.6) 0.000^†

Good 58 (34.7) 40.9 (4.8)

Moderate 75 (44.9) 37.4 (6.5)

Bad 19 (11.4) 34.9 (5.4)

Very bad 7 (4.2) 32.1 (8.5)

Exercise activity

No 101 (60.5) 38.1 (6.1) 0.003^‡

Once a week 39 (23.4) 37.8 (7.5)

Twice or three times a week 21 (12.6) 40.0 (6.1)

Everyday 6 (3.6) 42.5 (4.0)

Smoking

Yes 10 (6.0) 32.6 (6.8) 0.003^‡

No 157 (94.0) 38.8 (6.2)

Characteristics	n (%)	Mean (SD) score of WAI	P
Age group (years)
≤29	49 (29.3)	36.3 (7.5)	0.019^†
30–39	104 (62.3)	39.4 (5.6)
≥40	14 (8.4)	38.7 (7.0)
Gender
Male	150 (89.9)	38.0 (6.5)	0.004^‡
Female	17 (10.1)	42.1 (4.7)
Marital status
Single	26 (15.6)	38.4 (5.9)	0.968^‡
Married	141 (84.4)	38.4 (6.6)
Education level
Under diploma	21 (12.6)	37.0 (5.0)	0.453^†
Diploma	98 (58.7)	38.1 (6.9)
AD	16 (9.6)	39.2 (4.5)
BSc	29 (17.4)	39.6 (6.7)
Master’s and higher degrees	3 (1.8)	42.7 (4.2)
Sleep quality
Very good	8 (4.8)	43.9 (3.6)	0.000^†
Good	58 (34.7)	40.9 (4.8)
Moderate	75 (44.9)	37.4 (6.5)
Bad	19 (11.4)	34.9 (5.4)
Very bad	7 (4.2)	32.1 (8.5)
Exercise activity
No	101 (60.5)	38.1 (6.1)	0.003^‡
Once a week	39 (23.4)	37.8 (7.5)
Twice or three times a week	21 (12.6)	40.0 (6.1)
Everyday	6 (3.6)	42.5 (4.0)
Smoking
Yes	10 (6.0)	32.6 (6.8)	0.003^‡
No	157 (94.0)	38.8 (6.2)

^†Univariate analysis of variance (ANOVA); ^‡Independent t test. Note: WAI, work ability index; SD, standard deviation.

The workers’ mean (SD) score of WAI was 38.4 (6.4). Accordingly, 59 (35.3%), 35 (21%), 45 (26.9%), and 28 workers (16.8%) belonged to poor, moderate, good, and excellent levels, respectively. The relationships between the scores of the seven dimensions of WAI and its final score have been reported in Table 1. The results indicated that all dimensions had a significant relationship (p < 0.001) with the final mean score of WAI. Yet, ‘current work ability’ and ‘estimated work impairment due to diseases’ had the strongest association with the final mean score of WAI, with correlation coefficients of 0.67 and 0.65, respectively. On the other hand, ‘mental resources’ and ‘sick leave during the past year’ (with correlation coefficients of 0.45 and 0.46, respectively) had the weakest association with WAI.

The relationships between sociodemographic factors and the mean score of WAI have been presented in Table 2. Accordingly, age (p < 0.019), sex (p < 0.004), smoking (p < 0.003), and sleep quality (p < 0.000) were significantly associated with the mean score of WAI. The relationships between work-related factors and the mean score of WAI have been shown in Table 3. These results indicated a significant relationship between the mean score of WAI and work schedule (p < 0.002), conflict between the work and individual (p < 0.000), family (p < 0.003), and social (p < 0.00) lives, work injuries (p < 0.011), and job satisfaction (p < 0.000). In addition, the lowest mean (SD) scores of WAI were related to the workers with three-shift work schedules [30.3 (5.8)] and poor sleep quality [32.1 (8.5)]. In contrast, the highest mean (SD) scores were related to the workers with good sleep quality [43.9 (3.6)] and those with Master’s and higher educational degrees [42.7 (4.2)].

Table 3

The participants’ work-related factors and their relationships with the mean scoreof WAI (n = 167)

Characteristics	n (%)	Mean (SD) score of WAI	P
Job tenure (years)
≤4	68 (40.7)	39.0 (6.1)	0.276^†
5–7	74 (44.3)	37.9 (6.4)
≥8	25 (15.0)	38.5 (7.5)
Work schedule
Day-work	136 (81.8)	39.2(6.2)	0.002^†
Two- shift	28 (16.8)	35.6(6.6)
Three-shift	3 (1.8)	30.3(5.8)
Second job
Yes	6 (3.6)	35.5 (7.1)	0.26‡
No	161 (96.4)	38.5(6.4)
Overtime
Yes	151 (90.4)	38.3(6.3)	0.12^†
No	16 (9.6)	40.8(6.0)
Work hours (h/week)
<48	40 (23.0)	39.9(6.6)	0.175^†
49–70	91 (54.5)	38.3(5.8)
>71	36 (21.5)	37.2(7.6)
Work nature
Physical	41 (24.6)	37.3 (6.3)	0.133^†
Mental	24 (14.4)	37.0 (6.9)
Physical-mental	102 (61.2)	39.2 (6.2)
Workload
Light	4 (2.4)	41.7 (7.3)	0.305^†
Medium	64 (38.3)	39.1 (6.0)
Heavy	99 (59.3)	37.9 96.6)
Conflict between work and individual life
Very high	41 (24.5)	36.9 (6.8)	0.000^†
High	35 (21.0)	35.1 (7.1)
Moderate	68 (40.7)	40.5 (5.4)
Low	16 (9.6)	40.4 (5.0)
Very low	7 (4.2)	39.9 (4.9)
Conflict between work and family life
Very high	35 (21.0)	37.1 (5.3)	0.003^†
High	41 (24.5)	35.7 (7.2)
Moderate	57 (34.1)	40.1 (6.1)
Low	22 (13.2)	40.2 (5.8)
Very low	12 (7.2)	40.5 (5.1)
Conflict between work and social life
Very high	33 (19.8)	35.9 (6.4)	0.000^†
High	45 (26.9)	35.1 (7.0)
Moderate	54 (32.3)	41.4 (5.0)
Low	27 (16.2)	40.3 (4.7)
Very low	8 (4.8)	40.7 (5.5)
Occupational accidents and injuries
Yes	36 (21.6)	36.0 (7.5)	0.011^‡
No	131 (78.4)	39.1 (6.4)
Occupational training
Yes	85 (50.9)	39.3 (6.3)	0.074^‡
No	82 (49.1)	37.5 (6.4)
Job satisfaction
Yes	103 (61.7)	39.9 (5.9)	0.000^‡
No	64 (38.3)	36.0 (6.5)

^†Univariate analysis of variance (ANOVA); ^‡Independent t-test. Note: WAI, work ability index; SD, standard deviation.

4 Discussion

The findings of the current study showed that the participants’ mean score of WAI was good (WAI≥37). However, more than half of the participants (56.3%) did not have suitable work ability (WAI < 37) and belonged to moderate and poor work ability levels. Moreover, the results showed that sleep quality, conflicts between the work and individual and social lives, and job satisfaction had the most significant associations with the mean score of WAI.

Individual functional capacity, especially physical capabilities, start to decline after 30 years of age [2, 15]. A review of the studies conducted among workers in developed countries showed that older workers had poorer WAI scores compared to younger ones [16]. The present study results also revealed a significant relationship between age and WAI scores. Nonetheless, the workers aged ≤29 years had a lower mean score of WAI compared to those aged 30 years and above. Fischer et al. [9] and Chiu et al. [1] also came to similar results in their studies performed in developing countries. The observed discrepancy might be due to differences between developed countries (often have aged workforce) and developing ones (often have young workforce) regarding the working population’s age.

One of the most important findings of the present study was the significant relationship between WAI and sleep quality. The workers who had a very good sleep quality had higher WAI mean scores compared to those with very poor sleep quality. Problems and sleep disorders are among the important effective factors in health, which have been frequently mentioned in different studies [17 –20]. The results of the studies by Mokarami et al. showed that poor sleep quality had a strong effect on physical and mental health [14] as well as work ability [3]. Moreover, Lallukka et al. expressed that sleep disorders effected absence from work due to sickness [21]. These disorders can, in turn, have a negative effect on work ability. Similarly, Siversten et al. reported in a historical cohort study with a four-year follow-up period that insomnia was one of the independent and strong risk factors for disabilities after tiredness [22]. Consistently, Gharibi et al. conducted a study on Iranian workers and demonstrated a significant positive relationship between sleep quality and WAI scores [2]. They disclosed that poor sleep quality could cause chronic fatigue and loss of consciousness and increase the risk of accidents. In this regard, the current study findings indicated that the work schedule had a significant relationship with WAI scores. Accordingly, the workers with three-shift work schedules had very lower WAI mean scores compared to those with day and two-shift work schedules. Sleep problems and their consequences are among the most important problems among shift workers [19, 20].

The results of ANOVA indicated that conflicts between the work and individual, family, and social lives were significantly related to WAI scores. Accordingly, the WAI mean score was lower among the workers with the high conflict between work and life in comparison to those with the low conflict between work and life. Work hours and working a nonstandard work schedule are among the most important work-related factors that create conflicts between workers’ work and life [23, 24]. The results of the current study showed that the workers who worked more than 48 hours and had second jobs had lower WAI mean scores compared to other workers.

Two limitations of the current study were the cross-sectional survey design and utilization of self-report instruments. In addition, due to the fact that most of the study participants were male, aged under 40 years, and had a low job tenure, generalization of the results to all Iranian workers should be done with caution. Nevertheless, considering the young workforce structure and the prominence of male workers in most industrial work environments in Iran, the studied population may not be different from other workers of industrial environments in Iran. Yet, similar studies should be conducted among different age groups in other work environments in Iran. Finally, only some of the important work-related factors were investigated in the present study, while other risk agents for the workers’ safety and health might have affected the participants’ WAI scores, as well. Thus, these factors are recommended to be taken into consideration in future investigations.

5 Conclusion

Considering the mean age of the current study population, the WAI mean score was not suitable (WAI < 37) As a result, performing ergonomic and occupational health interventional programs is necessary in order to prevent early retirement and promote the workers’ work ability. According to the results of the current study, these programs should be concentrated on changing work schedules, not applying sensitive individuals in night shifts (those whose circadian rhythm stability and circadian rhythm amplitude is rigid type and languid type, respectively), improving sleep quality, and limiting work hours. Moreover, considering the relationships between different dimensions of WAI and its final mean score, the interventional programs are recommended to be concentrated on two dimensions of ‘current work ability compared to the lifetime best’ and ‘estimated work impairment due to diseases’.

Conflict of interest

The authors declare that there is no conflict of interest.

Contributors

All the authors have contributed substantially to data collection and manuscript preparation. No writing assistance from any agency has been employed in the preparation of this manuscript.

Funding

This study was conducted with financial support from Yasuj University of Medical Sciences.

Footnotes

Acknowledgments

The authors of this study would like to express their gratitude and appreciation to the management and workers of the company for their cooperation in conducting this study.

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