Translation, adaptation and validation of the Nurse-Work Instability Scale to Brazilian Portuguese*

Objective to translate, adapt and test the psychometric properties of the Brazilian Nurse-Work Instability Scale. Method this was a methodological study following the translation steps: synthesis, back-translation, specialist´s committee, semantics analysis, pretest, and psychometric tests. The committee was composed of 5 specialists. For the semantics analysis, 18 nursing workers evaluated the instrument and 30 pretested it. For the psychometric tests, the sample size was 214 nursing workers. The internal construct validity was analyzed by the Rasch model. Reliability was assessed using internal consistency, and concurrent validity with Pearson’s correlation between the Nurse-Work Instability Scale, and the Work Ability Index, Job Stress Scale. Results a Nurse-Work Instability Scale in Brazilian Portuguese with 20 items showed an adequate reliability (0.831), stability (p <0.0001), and an expected correlation with Work Ability Index (r = -0.526; P<0.0001) and Job Stress Scale (r = 0.352; p <0.0001). Conclusion the instrument is appropriated to detect work instability in Brazilian nursing workers with musculoskeletal disorders. Its application is fundamental to avoid long-term withdrawal from work by early identification of the work instability. Furthermore, the scale can assist the development of actions and strategies to prevent the abandonment of the profession of nursing workers affected by musculoskeletal disorders.


Introduction
Among health workers, the nursing personnel has globally experienced a significant number of work accidents and health problems (1)(2) . In this context, musculoskeletal disorders (MSD) stand out, since it has been related to decreased work ability (WA), disability, and absenteeism (3)(4)(5) . Additionally, considering that nursing workers perform activities with high physical demand (6) , it has been found that workers with occupational physical demand have an increased risk of disability, especially caused by MSD (7)(8) .
Moreover, the association of MSD with increased aging workforce (8) , and the presence of work stress (1) have been contributed to the shortage of nursing professionals, leading to an overload of the remaining workers and difficulties in staying at work (9)(10) .
One of the approaches to reverse this scenario is to plan ergonomic evaluation, intervention, and prevention strategies using the instrument Nurse-Work Instability Scale (Nurse-WIS) (9) . The Nurse-WIS was developed by a group of researchers from England (9) , based on the concept of work instability (11) .
The work instability is closely related to the risk of absenteeism due to illness, abandonment or change of profession. It is defined as the period when workers have increased difficulty in carrying out their activities, due to an incompatibility between their functional capacity and their work activities (11) . Thus, the concept of instability is understood considering a holistic conception, as it integrates physical and psychosocial elements, recognizing the relation between the individual requirements of work and the environment (12) . The psychosocial elements and work-related variables have been shown as important aspects to be considered in the assessment of workers with MSD when dealing with the risk of disability and of not remaining in employment (13) .
For nursing workers, the association between occupational factors, such as psychosocial and physical demand, and MSD was considered in the construction of the Nurse-WIS. The Nurse-WIS idealizers started building the scale by interviewing nursing workers with musculoskeletal disorders in a focal group (9)(10) , and followed the methodological steps of the Rasch model (14) to build and test the scale.
The reliability was tested using the Person separation index, showing an acceptable value of 0.9.
The test-retest showed a good agreement, with most of the items showing acceptable indices (0.62-0.75), using the Kappa statistic approach. Also, there were no significant changes between the scores obtained in the first and second moments analyzed, using the paired McNemar test (9) . Finally, the adequacy of the Rasch model was established according to the interaction trait of the Chi-square items with the p-value ≥ 0.001 (9) .
The instability classification, using the three cut-off points, was compared with the clinical classification of instability, evaluated by physiotherapists, and an index of 0.75 was found for sensitivity and 1 for specificity (9) .
In a prospective study on the German Nurse-WIS (15) , it was found that the scale could demonstrate an impending period of long-term sick leave, or pension for reduced work capacity, supported by a sensitivity of 73.9%, a specificity of 76.7%, positive predictive value of 26.6%, and a negative predictive value of 96.3%.
Thus, it was shown that it is possible to detect the level of instability at work caused by musculoskeletal disorders using the Nurse-WIS. Based on these results, the Nurse-WIS could be used as a management instrument to enable ergonomic evaluation and interventions, in order to prevent the loss of the individual's working capacity. The early identification of work instability is the key to avoid long-term withdrawal from work and to reduce the incapacity caused by musculoskeletal disorders (10) .
Previous studies (3)(4)(5) showed that musculoskeletal disorders are a global nursing workers problem leading to decreased work ability (WA), disability and absenteeism.
Thus, future studies directed to interventions of the consequence of musculoskeletal disorders are needed.
The Nurse-Work Instability Scale is an instrument that can be used to evaluate ergonomics intervention and prevention strategies to the absenteeism. In this way, the Nurse Work Instability Scale in Brazilian Portuguese advances in the knowledge of the instability caused by musculoskeletal disorders in nursing workers, since the study results will be able to be compared globally.
Although the Nurse-WIS showed good psychometric data, it is currently available only in English (9) and German (10) . Considering the detrimental consequences of musculoskeletal disorders, it is important to evaluate the work instability of nursing workers in different cultures (16) , including the Brazilian nursing population.  The target population was all nursing staff (nurses, nursing technicians, and nursing auxiliaries), of both sexes, located in outpatient clinics, wards, ICU, surgical centers, materials centers, and sterilization.
The inclusion criteria were working for at least one year in the nursing area, having had at least one episode of musculoskeletal pain in the last three months, lasting at least two hours. It is important to highlight that pain classification criteria was the same adopted by the group who created the Nurse-WIS (8) .
The exclusion criterion was to have other jobs outside the nursing area.
The sample was by convenience, through an approach performed at each workplace. The divulgation of the study was made in work environments, with the authorization of the head nurse, in all shifts and scales.
All procedures were explained for those interested and, if the worker, he or she was taken to a suitable place to answer the survey.
The study was divided into eight stages, following the steps recommended by international groups (9,(17)(18) (21) . The estimated sample size was calculated following the rule: the number of items in the Nurse-WIS multiplied by four to ten participants (21) . Thus, the sample size should be of 120 to 300 nursing workers.
In the psychometric stage, all participants All participants were oriented to answer the instruments and hand them over, in the sealed envelope, delivering it to the responsible researcher on the next day of work. If the researcher found unfilled items, the participant was approached again to answer these items.

Results
A total of 262 nursing workers participated in the study. In the semantic analysis, the mean age of

Discussion
The translation and cultural adaptation processes of an instrument is complex and must be performed carefully. In addition to the use of grammatically correct terms, adjustments might be made to the items and instructions for use. However, it is necessary to preserve the semantic, idiomatic, empirical and conceptual characteristics of the instrument and to obtain adequate psychometric properties (17) . Thus, following the procedures proposed by an international group (17) ,