Structured Multidisciplinary work Evaluation Tool (SMET) questionnaire: Translation,cultural adaptation and psychometric evaluation of the Persian version

Abstract

BACKGROUND:

To assess relevant environmental conditions in any work-setting requires a multidisciplinary perspective that is practical, valid, and reliable. This includes the physical, environmental, and psychosocial risk-factors. The Structured Multidisciplinary work Evaluation Tool (SMET) questionnaire simultaneously considers multiple work-related demands.

OBJECTIVE:

This study translated and culturally adapted the SMET into Persian and evaluated its psychometric properties in Persian industrial workers.

METHODS:

Cross-sectional translation and cross-cultural adaptation in five standardized phases. A convenience sample (n = 211) recruited from an industrial-occupation setting completed: the SMET; and the Rapid Upper Limb Assessment (RULA), and National Aeronautics and Space Administration Task Load Index (NASA-TLX) criteria; plus light and noise levels were concurrently assessed. Psychometric properties included: validity, with face (from confirmed language clarity, simplicity, and readability), content (via the content validity index, CVI, for equivalency and relevancy), criterion (through Pearson’s r correlation with relevant criteria), and construct (through known group validity between participants with/without work-related musculoskeletal disorders, WMSDs); internal consistency (Cronbach’s α); and test-retest reliability (intraclass correlation coefficient, ICC_2.1).

RESULTS:

Validity was confirmed with: face through the adaptation; content from suitable CVI values for items (CVI range = 0.78–1.0) and scale-total (CVI = 0.86); criterion from SMET associations with levels for light (r = – 0.42) and noise (r = 0.21), plus RULA (r = 0.42) and NASA-TLX (r = 0.39); and construct through participants with WMSD having significantly higher SMET total-scores (p = 0.01). Internal consistency (α= 0.89) and reliability (ICC_2.1 = 0.87) were acceptable and strong.

CONCLUSION:

This study indicated that the SMET Persian version had acceptable psychometric properties in an industrial occupational setting. Further investigation in longitudinal populations is recommended.

Keywords

Psychosocial demand physical demand reproducibility validation health outcome

1 Introduction

The importance of promoting safe and secure working environments is highlighted within the United Nations Sustainable Development Goals (UN-SDG) [1]. This is because workplace occupational health and safety (OHS) contribute to productivity and consequently have critical effects on the economy [2, 3]. The presence of work-related risk exposes employees to potentially uncomfortable working environments and potential work-related musculoskeletal disorders (WMSDs) [4]. The high incidence rate of WMSDs, recently reported at 27.2 per 10,000 workers, accounts for around 30% of all occupational injuries and illnesses that required days away from work [5, 6]. This is a significant public health concern [7] with notable costs to both industry and the working population [4, 8]. To recognize and screen for these risk factors the Structured Multidisciplinary work Evaluation Tool (SMET) questionnaire was developed in 2016 by Haraldsson et. al. [9] and provides a critical process that identifies then reduces risk, the subsequent incidence of WMSDs, as well as their associated economic and social costs [10].

The SMET is a practical questionnaire that assesses the work environment from a multidisciplinary/multifactorial perspective. It considers the workers perspective from the three most commonly experienced workplace related risk factors, those that are physical, psychosocial, and environmental. [9, 11, 12]. Consequently, the SMET differs from many other questionnaires that focus solely on one dimension of WMSD related risk factors. Further, the SMET incorporates an objective in-depth evaluation of workplace conditions that are performed by an OHS professional [12]. The SMET was validated in health workers using over 1000 employees and demonstrated excellent content validity for the full tool and its subscales [9], good trustworthiness, and intra-rater reliability (percent agreement (PA), 0.98–0.99) [11]. However, it has not been adapted and tested in different work-settings and populations, nor adapted for the Persian language and culture.

According to the Occupational Health Service Convention (No. 161, Part II Functions, Article 5b) provided by the International Labor Organization, OHS services should be based on: “Surveillance and identification of risk factors in the workplace which may affect the employees’ health” [13]. The multifactorial causation of WMSDs is commonly considered to include personal, physical, organizational and psychosocial exposures [14, 15]. Consequently, a preventative approach that detects risk factors related to the work setting, as employed by the SMET questionnaire, is a priority for the assessment of workplace risk [16]. However, most approaches to reducing WMSDs prevalence and unsuccessful outcomes in workplace settings focus on individual risk factors that are often evaluated in isolation. Examples of questionnaires developed to capture such situations include the ‘Job Content Questionnaire’ (JCQ) [17], ‘Copenhagen Psychosocial Questionnaire’ (COPSOQ) [18], ‘Occupational Health and Well-being Questionnaire’ (OHWQ) [19], the ‘Danish Psychosocial Questionnaire’ (DPQ) [20], ‘Quick Exposure Check’ (QEC) [21], and the ‘General Nordic Questionnaire’ (GNQ). Most of these questionnaires are ‘category-specific’ for risk related occupational health; though the COPSOQ, DPQ and JCQ have several dimensions and are respectively used for psychosocial risk prevention and occupational stress [17, 18]. Generally, the ‘combined hazards’ approach [22] receives minimal attention, which confounds the age-old adage that, ‘the whole is often greater than the sum of the parts’, as attributed to Aristotle (∼350BC) (and adapted by Koffka ∼1910 for Gestalt psychology theory). This is now recognized in 20^th century OHS as “ … the impact of the interactions may be far greater than that of any individual factor” [23].

Several barriers to effective workplace risk management are reported. These include misperceptions of the cause of WMSD, inadequacies in regulations and guidance for risk management, inadequacies in conventional OHS risk management paradigm, and inadequacies in WMSD risk management tools [24]. Incorporating valid and reliable tools that take a holistic ‘combined hazards’ approach, through the assessment and control of multiple risk sources, may resolve some of the highlighted inadequacies in WMSD risk management tools. This process can include the active participation of the worker through both the direct response to the SMET item-questionnaires and the provision of input through suggestions and comments to the three questions with an open-response option.

Iran, with a large working population of native Persian speakers that are employed across multiple industries, has a recognized high prevalence of WMSDs [25]. Identification of potential workplace health related risks from a culturally adapted perspective is required, but such an instrument must be reliable, valid, and both culturally and linguistically appropriate. A validated SMET Persian version (SMET-Pr) can be subsequently compared with findings from the original and other language versions. Therefore, the aims of this study were to translate and culturally adapt the SMET into Persian, perform this in an industrial Persian working population, and determine the critical psychometric properties of validity, internal consistency, and reliability.

2 Material and methods

2.1 Study design

This cross-sectional study was conducted in accordance with the published guidelines as described by Beaton et. al. [26], and the research was performed in a population of Persian workers from an industrial setting [27, 28].

Permission to translate and validate the SMET questionnaire was obtained from the original questionnaire developer, P. Haraldsson from Jönköping University, Sweden. All participants provided written informed consent to participate in the study and to permit data contributions towards publication. The Ethics Committee of the University of Social Welfare and Rehabilitation Sciences (USWR) (IR.USWR.REC.1401.096) approved the study.

2.2 Participants

The present study recruited 211 workers from a population of convenience at an auto-parts production and assembly company in Qom City, Iran, in 2021. Workers were employed in the production and assembly of switch, lighter, mirror, light, wire, press, actuator, and injection parts assembly and installation. This sector was sought for recruitment because of the high reported rate of WMSDs being prevalent in their annual medical examination report. The employees’ tasks usually included the dual activities of manual handling (assembly work) and non-manual work (use of automatic devices). The inclusion criteria were: (1) employed in the same job for the preceding 12 months; (2) aged 18–55 years; (3) willingness to voluntarily participate in the study; and (4) ability to read and understand the questionnaire items in the Persian language.

2.3 Instruments

2.3.1 Structured Multidisciplinary work Evaluation Tool (SMET) questionnaire

The SMET questionnaire was developed and validated through a multifactorial approach using action research planes between 2008 and 2016 year in a population of healthcare workers [9]. The reliability of the SMET questionnaire was subsequently evaluated in 2019 in a further population of health workers [11]. The SMET questionnaire is a 30-item instrument that assesses three workplace domains: physical demands (9-items), environmental demands (8-items), and psychosocial demands (13-items). In each domain, the individual is asked to rank the questions in the order of ‘worst’ demands and an open question is provided relating to the individuals perceived ‘most strenuous work’ situation/s. An 11-point (0–10) numeric scale is used for scoring which is anchored at 0 = ‘desirable’ workplace status and 10 = ’worst’ [9].

2.3.2 Rapid Upper Limb Assessment (RULA)

The RULA is an observational tool used extensively to investigate the risk factors of WMSDs on the upper extremities [29]. A single score provides a “snapshot” of the task which is extracted from the tool with the risk score of the work conditions defined. The tool has a summated total ranging from one (low risk) to seven (high risk) that is determined from four sub-scores of A through D where: A groups the upper arm, lower arm and wrist postures; B groups the neck, trunk and legs postures; C is ‘Score A’ + ‘muscle use’ and ‘force scores’; D is ‘Score B’ + ‘muscle use’ and ‘force scores’. The RULA has demonstrated good reliability and validity in previous research [29, 30].

2.3.3 National Aeronautics and Space Administration Task Load Index (NASA-TLX)

The NASA-TLX is a commonly employed self-reported measure of mental workload evaluation. It is a multi-dimensional scale with six subscales including mental demand, physical demand, temporal demand, performance, effort, and frustration [31]. Each of the five dimensions are rated for the level of demand on a 7-point scale. Increments of high, medium, and low estimates for each point result in 21 graduations on the scales.

2.4 Translation and cross-cultural adaptation of the SMET

Five standardized steps of the translation and cross-cultural adaptation process (forward, synthesis, backward, consolidation, and pre-final version testing) were adopted [26].

Step-1 forward translation, this was performed by two independent native Persian translators. One translator (PhD of Ergonomics) was familiar with the concepts and fluent in English (T1) and the second was blinded (T2).

Step 2 a synthesized version of the SMET questionnaire, this was developed by one of the translators (T1) and one of the researchers (HR.M).

Step-3 backward translation, this involved two additional bilingual independent translators with no knowledge of the SMET questionnaire who translated the synthesized version back to English (T3, T4).

Step-4 consolidation, this involved a 10-person expert committee that included a physiotherapist, two occupational health engineers, one ergonomist, an occupational medicine specialist, the four translators and a methodologist. The committee reviewed the two back-translation versions and compared them with the original version. As the aim of the current study was adaptation of the SMET questionnaire from a health setting to one of an industrial occupational, in item 14, the chemical materials were replaced with those commonly used in the auto-parts industry. After verification of the semantic, idiomatic, grammatical, and conceptual equivalence between the versions, a pre-final consensus version was reached for the Persian SMET questionnaire for a pilot study.

Step-5 pre final version, this was sent to the developer of the questionnaire (Haraldsson) to confirm its equivalency with the original version.

In the pilot stage, the SMET questionnaire was presented to a sub-sample of 30 workers (mean age = 28.4±5.6) selected on a convenience basis in order of presentation and availability. These participants were requested to read and carefully complete the Pre-final ‘Persian version of the SMET questionnaire’ (SMET-Pr)). Through an interview with each worker a written report was produced concerning the: misunderstandings, item ambiguity and any inability to answer item-questions. The high proportion of missing items or misunderstood words were evaluated, and final adaptations were made by the expert committee. The final SMET-Pr questionnaire was developed and used for the process of psychometric evaluation.

2.5 Psychometric assessment of the SMET-Pr questionnaire

2.5.1 Face validity

The face validity of the SMET-Pr was obtained through a qualitative analysis of the n = 30 workers comments extracted from the pilot testing. This involved the expert panel of eight professional as detailed earlier. The consensus on the relevance of content, clarity of language, simplicity, and readability was obtained.

2.5.2 Content validity

Content validity is the degree to which a test or assessment instrument evaluates all aspects of the construct that it is designed to measure. The content validity index (CVI) is commonly used as a quantitative method of evaluation [32]. At the levels of the items (I-CVI), subscales (SS-CVI) and scale (S-CVI), this characteristic was calculated for each perspective to demonstrate the content equivalency and relevancy of the SMET-Pr. The eight members of the expert panel from the face validity section participated in this and rated the content relevancy on a 4-point scale (from 1 = not relevant to 4 = very relevant). The proportion of experts giving items a relevance rating of 3–4 is considered as the cut-off for I-CVI. The SS-CVI and S-CVI were determined by their mean scores from all eight assessments [33, 34]. An acceptable CVI value score from > eight experts is 78% [33].

2.5.3 Criterion validity

In this study we assessed the criterion validity of the environmental subscale by comparing the correlation with the recognized standardized instrumental measured values for noise (noise dosimetry) and, and light (lux meter).

The subscales values for criterion validity were each compared with the relevant accepted and recognized standards using a Pearson’s r correlation coefficient where values > 0.70 indicated acceptable criterion validity [34].

The environmental subscale (noise and light). According to Iranian occupational exposure limit standard, the limits for eight hours of daily work are: occupational noise is 85 dB; and intensity of local illumination is 300 Lx [35–37]. If the worker is exposed outside the recommended limits then technical control measures are recommended to be implemented to reduce noise exposure or improve lighting [35, 36].

The physical demand subscale score was correlated with the RULA score and the physical demand subscale of the NASA-TLX.

The psychosocial demand subscale was correlated with the NASA-TLX total score to determine the mental workload component.

2.5.4 Construct validity

Hypotheses testing was used for investigating the construct validity of the SMET-Pr. We expected to find some correlation between the SMET-Pr and selected subgroups of participants ‘known-group’ validity. The SMET-Pr was administrated to two groups of subjects with and without a WMSDs history, and the mean scores of the SMET-Pr were subsequently compared. The hypotheses was that subjects with a WMSDs history would have a higher total SMET-Pr score and also for the related subscales. An independent T-Test was used to determine the construct validity in these two groups.

2.5.5 Reliability

Two aspects of reliability were considered, the internal consistency and the test-retest reliability. The internal consistency of the total items and subscales were evaluated with Cronbach’s Alpha (α) and the related 95% confidence intervals. An α≥0.70 is recommended as an acceptable cut-off value to determine satisfactory internal consistency reliability with a limit of > 0.95 indicating redundancy [34, 38].

To evaluate test-retest reliability the SMET-Pr was repeated after 3–7 days in a sub-sample of n = 50 workers. The intraclass correlation coefficient (ICC _2,1) for the SMET-Pr total score and each of the subscales’ scores were computed. An ICC value > 0.75 indicated strong reliability [38].

3 Results

3.1 Phase-I: Translation and cross-cultural adaptation

Translation and cultural adaptation of the SMET questionnaire raised idiomatic issues for six items during the pilot testing process. The expert committee determined a consensus and established face validity. The following revision and modifications changes were accepted and applied:

1. Item 3, the “unilateral or fixed working positions” was not understandable in the Persian context and with clarification by the original developer it was changed to “fixed static positions for prolonged time such as sitting or standing”.

2. Item 4, the “uncomfortable working positions” was unclear and for clarification it was modified to include additional examples such as “neck or lumbar bending and twisting, over shoulder activity”.

3. Item 6, the “vision demand” was unclear in the Persian context and with clarification from the original developer and the expert panel the final consensus was that “prolonged display work, visual accuracy, work focus” be added in parentheses.

4. Item 11, the “draft” was not familiar in the Persian language and following clarification from the original developer it was replaced with “indoor air ventilation”.

5. Item 14, some chemical risk factors are reported which are mostly found in hospital settings, but this adaptation was for use in the industrial workplace and required added related chemicals examples for clarity for employees. Consequently, to achieve this we added the terms “Toxic gases and vapors, solvents, pesticides, toxic metal dust”.

6. Item 19, lacked clarity on what feedback was from whom. Therefore, we added feedback from both “managers and/or colleagues”.

All changes were made based on the pilot study feedback from the 30 participants’ and after the expert panel discussions and a consensus decision. These processes were consequently able to achieve the required face validity. The translated Persian SMET is the intellectual property of the questionnaire developers and is available by direct contact with the authors.

3.2 Participants

The demographic characteristics of the participants (n = 211) are presented in Table 1. There was a higher proportion of male participants (n = 124, 58.8%, age = 33.76±0.63 years) than female (n = 87, 41.2%, age = 32.24±0.69 years).

Table 1
Socio-demographic characteristics of participants (n = 211)

Variable Number (%) Mean (SD)

Age (year) 211 33.97±6.86

Job history (year) 211 3.92±4.16

work duration (hours per day) 211 11.00±0

Height (m) 211 1.69±0.09

Weight (kg) 211 72.93±15.69

BMI 211 25.46±4.88

Gender Male 124 (58.8) 33.76 (0.63) years

Female 87 (41.2) 32.24 (0.69)

Marital status Married 109 (51.7) –

Single 102 (48.3)

Education Under high school diploma 60 (28) –

Diploma 110 (52.1)

Associate Degree 9 (4.3)

Bachelor’s Degree 32 (15.2)

Occupational Employee 105 (49.8)

status Nonemployee 62 (29.4)

Retired 44 (20.8)

Variable	Number (%)	Mean (SD)
Age (year)	211	33.97±6.86
Job history (year)	211	3.92±4.16
work duration (hours per day)	211	11.00±0
Height (m)	211	1.69±0.09
Weight (kg)	211	72.93±15.69
BMI	211	25.46±4.88
Gender	Male	124 (58.8)	33.76 (0.63) years
	Female	87 (41.2)	32.24 (0.69)
Marital status	Married	109 (51.7)	–
	Single	102 (48.3)
Education	Under high school diploma	60 (28)	–
	Diploma	110 (52.1)
	Associate Degree	9 (4.3)
	Bachelor’s Degree	32 (15.2)
Occupational	Employee	105 (49.8)
status	Nonemployee	62 (29.4)
	Retired	44 (20.8)

Table 2

Evaluation of criterion validity of the SMET-Pr questionnaire

The SMET-Pr	Criterion	Correlation (r)	Significance (p)
Physical subscale score	RULA score	r = 0.42	p = 0.006
	NASA-TLX physical score	r = 0.39	p < 0.001
Psychosocial subscale score	NASA-TLX total score	r = 0.35	p < 0.005
Environmental subscale score	Light levels	r = – 0.42	p < 0.001
	Noise levels	r = 0.21	p = 0.08
Item 10 (problems with noise levels)	Noise levels	r = 0.20	p < 0.005
Item 12 (problems with lightning)	Light levels	r = – 0.025	p < 0.001

The RULA, NASA-TLX physical score and total score, light levels and noise levels were used as external criteria. Criterion validity was evaluated with Pearson's correlation coefficient (r). Statistical significance (p) was evaluated with Students T-test.

Table 3

Evaluation of construct validity of the SMET-Pr questionnaire

The SMET-Pr	Construct	Effect size (MSD yes/no score)	Significance (p)
Total score	MSD history (no)	125.16 (23.82)	p = 0.01
	MSD history (yes)	137.17 (25.19)
Physical subscale score	MSD history (no)	46.17 (10.10)	p = 0.001
	MSD history (yes)	50.61 (9.10)
Environmental subscale score	MSD history (no)	19.33 (7.00)	p = 0.2
	MSD history (yes)	19.21 (8.15)
Psychosocial subscale score	MSD history (no)	60.65 (14.89)	p = 0.01
	MSD history (yes)	67.34 (13.51)

WMSD history (yes/no) was used as external construct. The SMET-Pr score in relation to WMSD history (yes/no) was used for effect size. Statistical significance (p) was evaluated with Students T-test.

3.3 Psychometric assessment of SMET-Pr

3.3.1 Content validity

The results of I-CVI (range 0.78–1.0) and S-CVI (0.86) were acceptable, exceeding the required cut-off. The SS-CVI for physical (0.90), environmental (0.95), and psychosocial (0.85) were similarly acceptable.

3.3.2 Criterion validity

There was a negative significant correlation between the SMET-Pr environmental subscale score and light levels (r = – 0.42, p < 0.001). The correlation between noise level and SMET-Pr environmental subscale score was positive but not significant (r = 0.21, P = 0.08). To confirm the correlation between these two variables, a correlation between the item 10 and noise level (r = 0.20, p < 0.005) and between item 12 and light level (r = – 0.025, p < 0.001) were performed. Item 10 is “Do you experience any problems associated with high noise levels at your workplace?” and Item 12 is “Do you experience any problems associated with the lightning in your workplace?”. The correlation between these two variables was confirmed.

In relation to the remaining subscales, there was a significant correlation between the physical SMET-Pr subscale score and the RULA score (r = 0.42, p = 0.006) and a significant correlation between the physical SMET-Pr subscale and the physical demand subscale of the NASA-TLX (r = 0.39, r < 0.001). Further, the correlation between the score of the psychosocial demand of SMET-Pr subscale and the NASA-TLX total score was significant (r = 0.35, p < 0.005).

3.3.3 Construct validity

The results of the independent T-test to determine known group validity showed that the subjects with WMSDs history had a significantly higher SMET-Pr for their total score (p = 0.01) and two of the three subscale scores, namely physical (p = 0.001) and psychosocial (p = 0.01). These findings demonstrated acceptable construct validity. The environmental subscale score was not significant between the two groups (p = 0.2) indicating there was no support for the environmental subscale.

3.3.4 Reliability

The questionnaire internal consistency was indicated as acceptable from the reported Cronbach’s alpha values for: total items = 0.89, psychosocial demand = 0.89, environmental demand = 0.76, and physical demand = 0.74.

The test-retest reliability was strong (ICC = 0.87, CI = 0.83–0.91) with the ICC for the three demands being physical = 0.95 (CI = 0.92–0.97), psychosocial = 0.89 (CI = 0.81–0.94), and environmental = 0.93 (CI = 0.89–0.96).

4 Discussion

To understand the effects of the complexity of work conditions on human health, consideration is required of the different aspects of physical, mental, psychosocial and environmental demands [39]. The SMET questionnaire is the only questionnaire that has taken a multidisciplinary/multifactorial approach in the evaluation of workplace conditions. In addition, this study is the first to provide a new version of the SMET in a work setting that is different from that of the original health care environment. Consequently, the SMET-Pr culturally adapted and translated for the Persian auto-parts workers population (SMET-Pr) and has potential application to this and related industrial settings which has expanded the potential for the SMET. During the process of translation and cross-cultural adaptation several changes were made. The implementation process involved a consensus expert committee approach to improve and enrich the comprehensiveness of the SMET-Pr [26]. This is a required process for any instrument to be applied in order to ensure the similarity of work results across different cultures [40]. In addition, some changes were related to the SMET-Pr adaptation from the health care to the industrial environment. Consequential changes are necessary as highlighted in Item 14, as chemicals used in industrial environments are different to those in the hospital environment.

In the pilot study, face validity demonstrated that the Persian industrial workers had difficulty understanding concepts such as “draft”, “uncomfortable positions”, “unilateral positions”, “vision demand” and “feedback”. The individuals completing the questionnaire must be able to understand the construct and content of the instrument in order to provide a real assessment of their work environment. In order to clarify the ambiguous concepts perceived by the workers some explanations relating to these items were added in parentheses. Since no previous translation and cultural adaptation had been performed it was not possible to compare the results with any previous studies. However, when compared with the original SMET questionnaire version, the SMET-Pr demonstrated excellent face validity through the process of questionnaire items discussion with experts who had the relevant scientific knowledge and field experience [9].

In this study, assessment of the content validity was performed though a quantitative method by calculating the CVI at both the item and total level. This is an expert committee-based process where suggestions are provided and implemented to determine the instrument-items relevancy. The acceptable CVI cut-off of 78% was achieved in this study for a minimum eight-person expert panel [33]. Further, all three subscales had excellent relevancy to the SMET-Pr score, indicating that environmental, physical, and psychosocial factors were related to being workplace risk factors. Subsequent criterion validity results confirmed this relevancy, where correlation between each subscale and the related criterion measure was also validated. The results are comparable to those of the original study where the S-CVI (0.89) approximated to the SMET-Pr result (0.86). In addition, the calculated CVI for three the subscales of physical, environmental and psychosocial in the original study, were respectively 0.90, 0.83 and 0.92 [9] which again reflected closely on the respective SMET-Pr subscale results of 0.90, 0.95 and 0.85.

The SMET-Pr demonstrated a strong agreement among the participant’s answers for test-retest reliability, with high ICC values for all subscales that reflected those shown in the original version. The original SMET questionnaire showed high percentage agreement (PA) with low variability for all subscales that demonstrated this reliability [11]. An instrument’s test-retest reliability is critical in detecting the risk factors of the work environment in both the initial and any follow-up reevaluation and in justifying or determining the effectiveness of any applied intervention/s [41].

The SMET-Pr also demonstrated acceptable internal consistency (α= 0.89), which implies that the instrument is evaluating total as well as different aspects (physical, environmental, and psychosocial) of the work environment. This in-turn supports the premise that the instrument items do measure the same characteristic without the presence of item redundancy [41].

The SMET questionnaire is a self-estimating or patient reported questionnaire that is unique as a multidisciplinary evaluation of work conditions, which means that there is no available ‘gold standard’ criterion. Consequently, to meet this psychometric requirement a comparison between the face and content validity of the SMET questionnaire and a comparable instrument was not possible. To overcome this, evaluation of the criterion validity was demonstrated through the comparison of the SMET-Pr item’s scores with the appropriate technical and subjective measurement criteria. Specifically, technical measurements of noise and light were conducted through noise dosimetry and the use of a lux meter. The degree of work-related problems (item 10 and 12, p = <0.005) and the environmental sub-score also correlated with noise and lighting measurements. This correlation implies that noise and lighting that fail to meet the recommended standards can lead to work-related problems being experienced and subsequently excess environmental work demands. It was reported in previous research that there is a correlation between subjective and objective assessments of the environmental conditions in the workplace, with recognized agreement between worker’s’ estimation of their environmental conditions and the objectively measured noise and illuminance levels [42]. Consequently, our results indicated that the workers’ assessment related to their own environmental conditions through the SMET-Pr is a genuine reflection of the actual workplace conditions and supports previous findings of correlations between quantitative and qualitative measures [42].

The study also showed a significant correlation between the physical self-estimated SMET-Pr and RULA scores, and the physical demand subscale of the NASA-TLX. The RULA was developed to “rapidly” evaluate the exposure of individual workers to ergonomic physical risk factors associated with upper extremity WMSDs. As most of the study participants were employed in montage workstations requiring upper limb manual handling, the RULA is a relevant and adequate physical work demand valuation instrument [43]. The reported significant correlation between the SMET-Pr and RULA implied that the higher the RULA score, the greater the work-related problems the workers would experience in terms of their physical work demands.

Psychosocial risk factors are categorized as psychological demands, influencing control over work demand, support from co-workers and management, work satisfaction, work rewards, unreasonable work demands, and job security. These constructs influence the worker’s capacity as well as their health and performance in the workplace [44]. Mental workload as measured by the NASA-TLX questionnaire mental health subscale, acts as a proxy for psychosocial factors as it is an instrument with multidimensional constructs that include the six subscales of mental, physical, temporal demand, effort, performance, and frustration [45]. Mental workload is one the most important psychosocial factor considerations that are recognized as being positively correlated [44, 46]. Our results confirmed this demonstrating a correlation between the mental workload and that of the workplace psychosocial risk factors. Consequently, the findings support the acceptance of criterion validity through the SMET-Pr psychosocial subscale.

Construct validity was demonstrated by a statistically significant difference between two groups of subjects with and without a history of WMSDs. It was hypothesized that the physical [4], environmental, and psychosocial work demands [4, 47] would be higher in subjects with a history of WMSDs. The physical and psychosocial factors demonstrated these effects’ as being significant, but the environmental demand was not. This suggests that the SMET-Pr distinguished between subjects who were in work situations that were physically and psychosocially demanding and could have the potential to lead to the development of musculoskeletal disorders. Such an assumption would need to be tested in further longitudinal research.

4.1 Study Strengths and Limitations

The study strengths include the linguistic and cultural adaptation of the SMET to the Persian Language. Further, the validation was made in a new occupation-specific setting, that of the industrial setting of auto-parts workers. This industry-specific application was required due to the participant recruitment process and achieved through the use of content validity assessment using the CVI.

Consequently, some limitations of the current study should be noted. Generalizability is limited to those occupational settings in which the SMET has been validated, namely healthcare and now the industrial setting of auto-parts workers. This has potential implications for industrial and assembly line occupational settings with equivalent physical and psychosocial occupational demands that may potentially use the SMET as it has now been validated. Further, the study results are subject to recall bias that occurs from individual over-estimation and under-estimation of responses due to the questionnaire’s self-report nature. This cross-sectional study does not allow conclusion of a causal relationship between the occupational health risks and the WMSDs. Future longitudinal research is required to resolve this limitation.

While the psychometric properties of the SMET questionnaire, such as construct, criterion, and content validity were confirmed, other forms of validity such as structural validity through factorial and Rasch analysis should be examined, however the statistical process for doing so must consider the multiple scaling and open-item nature of the SMET questionnaire design. Although participants with different manual and non-manual tasks were recruited to the study, our sample composition may limit the external validity of our results and should be cautiously generalizable to other workers and tasks as detailed above. Future studies are needed to confirm the stability of the tool by evaluating the psychometrics properties on a larger sample from multiple industries with different task conditions.

5 Conclusion

The SMET questionnaire uses a multidisciplinary/multifactorial approach to determine occupational health risks. The instrument was successfully and validly translated and culturally adapted into Persian based on standardized guidelines in order to provide the SMET-Pr. The test-retest reliability of the subscales and total score were both demonstrated as strong. The known-groups technique verified the construct validity for workers in an automotive parts production and assembly company in Iran. Our findings consequently support the usability of the SMET-Pr as a multidisciplinary evaluation method in the industrial work environment in Iranian people as a reflection of the Persian population. The experience of the workers related to their working conditions, as assessed by the SMET-Pr, can be considered as a subjective method that has greater simplicity and time efficiency than objective workplace evaluation methods.

Footnotes

Ethical Approval

The study was approved by the Ethical Committee of the University of Social Welfare and Rehabilitation Sciences (USWR) (IR.USWR.REC.1401.096).

Informed consent

Informed consent was obtained from all individual subjects included in the study.

Conflict of interest

All authors declare that they have no conflicts of interest.

Funding

The research protocol was approved and supported by the student research committee at the University of Social Welfare and Rehabilitation Sciences, Tehran, Iran (grant number: 2814).

Acknowledgments

The authors appreciate the financial and technical support of the student research committee at the University of Social Welfare and Rehabilitation Sciences, Tehran, Iran. The authors are also grateful to the volunteers for their participation.

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