Introduction

It is known that the use of software and applications for mobile devices is growing daily ¹, and one of the fields in which this advancement stands out is healthcare ². When creating a computer system for use on computers or mobile devices, the developer is expected to evaluate the usability, that is, investigates the ease with which users can perform specific tasks when interacting with such systems. Therefore, it is necessary to use appropriate methods and tools to improve what has already been developed and provide broader access to these resources ³. More than 242 million mobile phone lines currently exist in Brazil ⁴, demonstrating the need to develop solutions based on mobile devices and advancing studies to measure usability, specifically for computer tools ⁵.

Considering the significant amount of software and applications, it is necessary to evaluate their usability by instruments that can be widely used and adapted to the Brazilian Portuguese language and culture. The usability scales employed internationally include the Usability Measurement Inventory software, which measures user perception of usability and compares software versions ²; the Standardized User Experience Percentile Rank Questionnaire, which evaluates usability, trust, appearance, and loyalty ⁶, and the Questionnaire for User Interaction Satisfaction, which considers subjective user satisfaction with specific aspects of the human-computer interface.

In Brazil, the Questionnaire for User Interaction Satisfaction and the System Usability Scale measure software usability; both are used through free translation ⁷, lacking professional translation and cross-cultural validation procedures.

Therefore, it is relevant to translate and cross-culturally validate into Brazilian Portuguese, with adaptation to the Brazilian context, a usability scale with psychometric properties previously evaluated in other contexts and that proves to be valid and reliable, as well as simple and easy to use. We found that a scale with such characteristics exists, used internationally to measure software usability, including the nursing field ⁸: the System Usability Scale ⁹, which has already been translated and validated into European Portuguese ¹⁰. This version has also been used in Brazil.

It should be noted that the System Usability Scale is simple, consisting of only ten objective statements. They provide an overview of the user's usability evaluation and can be applied to several products and services, such as websites, mobile applications, and clinical systems.

Within the usability evaluation methods described in the literature, questionnaires assume significant importance for collecting self-reported qualitative data on users' characteristics, thoughts, feelings, perceptions, behaviors, or actions ¹⁰. This scale has drawn the attention of researchers for its benefits, such as ease of use, evaluation of different tasks within the same interface (system screens), compar ison of versions of the same system, and comparison of competing implementations ^8-11.

A growing number of health care researchers, especially in nursing, have been involved in the development of software, systems for the electronic registration of care, and mobile devices for use by professionals, patients, and the public. However, it is crucial to evaluate the usability of these systems and applications, depending on their type or purpose. The literature indicates that usability assessment though the System Usability Scale questionnaire is a valuable strategy to verify the interaction between application and system users and used in several fields, including nursing ¹². It is worth noting that the System Usability Scale can be applied to evaluate usability in any system or application, not only in healthcare.

Thus, this study aims to perform the cultural adaptation of the System Usability Scale for the Brazilian Portuguese language and evaluate its internal consistency and structural construct validity.

Materials and methods

Results

Two rounds of evaluation with the experts were necessary. In the first round, four items required discussion to reach a consensus. Item 1 of the System Usability Scale, "I think that I would like to use this system frequently," translated as "Eu gostaria de usar esse sistema frequentemente," was considered non-equivalent to the original by one of the specialists for lacking the phrase "eu acho que." Item 4, "I think that I would need the support of a technical person to be able to use this system," demanded adjustments, as the Portuguese version included the word "eu" twice, just as the English version, which was considered unnecessary by a specialist. Regarding item 7, "I would imagine that most people learn to use this system very quickly," approaching semantic equivalence and considering the grammar (partitive collective), the consensus among researchers and specialists led to the wording of "Eu imagino que a maioria das pessoas pode aprender a usar esse sistema muito rapidamente." For item 9, "I felt very confident using the system," the final wording was "Eu me senti muito seguro usando o sistema."

Following the adjustments made by the specialists, the modified version was sent to everyone for a second round and approved. This version, considered the pre-final version of the System Usability Scale in Brazilian Portuguese, is presented in Table 1 and was used in the test. At the end of this process, the proposed title for the adapted version was "Escala de Usabilidade de Sistema - versão brasileira" (System Usability Scale - Brazilian version).

It is reported that no suggestions for changes or comments regarding difficulties in comprehension were made. The Brazilian version of the System Usability Scale presented an acceptable level of reliability, with Cronbach's alpha equal to 0.76.

A KMO value of 0.73 for the instrument and a p-value lower than 0.0001 in Bartlett's Test of Sphericity were obtained for structural construct validity, indicating that the exploratory factor analysis was adequate. The results suggested a structure composed of three domains, which combined would explain 64.64 °% of the variance in the principal component analysis and 51.55 °% in the common factor analysis (Table 2).

Table 3 presents the factor loadings of the items in each factor of the principal component analysis after applying the Varimax rotation method. Table 4 presents the factor loadings of the structure matrix and the standard matrix obtained by the common factor method after applying the Direct Oblimin rotation. The results obtained suggest the same distribution of items among the three factors.

In Table 5, where the communality values obtained for each of the methods used are presented, it can be noted that some items have low communality values.

We verified that the evaluations of the factorial solutions obtained were not satisfactory, either through the indexes obtained or through the domain structure formed, which was not adequate from a practical point of view. Based on this, the decision was to keep the instrument's original version (unidimensional).

The internal consistency was also evaluated through Cronbach's alpha coefficient. This coefficient varies from 0 to 1, where values greater than 0.7 indicate reliability between measures.

Discussion

The translation process carried out with the method recommended by the literature enabled the achievement of a final version entirely understandable by the test participants. This study also confirmed the unidirectionality of the scale and an indication of the well-defined structure as proposed initially.

We believe that this study came across the need for a Brazilian version of the System Usability Scale, as it is a helpful instrument that has been applied in the Brazilian context ^3,8, but without a version that had formally undergone the cross-cultural adaptation process. The specialists' committee proved to be consistent with the study's objectives and the context of the System Usability Scale, as recommended by the literature ¹³.

The psychological test adaptation procedure was performed to translate the System Usability Scale into Polish ¹⁸. A Cronbach's alpha value of 0.805 was also identified, with high correlations between the Polish and English versions' items and the total score.

The Malaysian version of the System Usability Scale ¹⁹ was developed from a front-to-back translation of the scale. The final version was reached through consensus and cross-cultural adaptation with ten specialists in mobile application development. The content validity index was found to be 0.91, indicating the relevance of the ten items of the System Usability Scale to evaluate the usability of mobile device applications. Face validity was also analyzed with ten cell phone users, obtaining a value of 0.94, indicating that the scale was easily understood. Reliability was assessed among 54 cell phone users, reaching a Cronbach's alpha value of 0.85 (95 % confidence interval; 0.79-0.91), which denotes a reliable version for its proposed assessment ¹⁹.

On the one hand, the System Usability Scale provides a usability score easily understood by many people: project managers, computer programmers, and application users. It becomes apparent, on the other hand, as its author rightly puts it, that the scores for the items are not meaningful by themselves ⁹. Therefore, the usability evaluation should be understood based on the set of answers to the items of the System Usability Scale. It has been noted; however, that software users and IT professionals tend to ignore this recommendation provided by the scale's author ^20-22 and often consider, in isolation, information regarding the quality of specific aspects of usability, viewing the evaluation obtained through some items of the scale. This study confirmed the one-dimensionality of the System Usability Scale, which reaffirms the original author's recommendation that its items should not be analyzed separately.

A recent study ²³ has found that the use of mobile devices by nurses is increasing, considering a sample of 24 studies (19 master's theses and five dissertations) that verify the development and use of applications: 16 (66.7 %%) of them with a care focus, six (25 %%) with an educational focus, and two (8.3 %%) with a management focus.

From the automotive sector to space and industrial research, from people with different disabilities to voters, many sectors are interested in conducting usability research ^{(9, 10)}. In nursing care and in light of the swift technological development in healthcare, it is believed that this scale can be used in different contexts.

Conclusions

The System Usability Scale cross-cultural adaptation process into Brazilian Portuguese was conducted according to the steps recommended by the literature. For the adapted version, the title "Escala de Usabilidade de Sistema - versão brasileira" (System Usability Scale - Brazilian version) was adopted. The cultural adaptation process demanded only a few adjustments in some terms concerning the original version. The Brazilian version of the System Usability Scale was user-friendly and easy to understand, confirming its functionality. It also presented construct validity, being equivalent to the original English version.

As a limitation, the test was carried out at a single private university, with students from two courses, and focused only on the WhatsApp application. Studies involving the testing of other systems and other target audiences are suggested to confirm this version's adequacy, considering the country's cultural diversity. Another limitation of the study is that the participants were not randomly selected. Furthermore, as the results suggested a one-dimensional factor structure, it is recommended that the structural construct validity be assessed again using the item response theory technique in a future study.

Therefore, it is believed that the System Usability Scale can be used to evaluate new technological tools, such as computer programs and software for teaching and care in healthcare and nursing.