To solve the research objectives, we choose a mixed research method including qualitative research at an early stage and quantitative research at a later stage.

Auditing with RBA has become popular in developed countries but the topic is new in developing countries such as Vietnam. Therefore, this study was conducted to identify factors influencing RBA implementation and the quality of independent audit in Vietnam. The research results indicate that six factors have positive relationships with the level of applying the RBA and the quality of independent audit, including: capacity of auditor, job pressure on auditor; the support of IT; competitive capacity of audit firms; audit fees and client's risks. This result is similar to the findings discovered by previous studies such as Al-Khaddash, Al Nawas and Ramadan (2013), and Danescu and Chira (2014). However, it is important to note the impact of factors on the level of RBA application, and independent audit quality. Based on the Estimate coefficient in Table 6, the impact level of the factors on RBA application in the descending trend is arranged as follows: client's risks (0.199), capacity of auditor (0.188), competitive advantage of audit firms (0.164), the support of IT (0.143), job pressure on auditor (0.111), and audit fee (0.086). The gradual influence of the factors on audit quality is as follows: RBA (0.441), the support of IT (0.118), capacity of auditor (0.112), client's risks (0.105), job pressure on auditor (0.097), and competitive advantage of audit firms (0.089). With these results, some points need to be discussed:

In literature as well as practice, it has been showed that the capacity of auditors is one of decisive factors influencing on the audit quality (Boon et al., 2008; Do, 2015). Furthermore, performing an audit under RBA requires auditors to make more professional assessments of what is considered important and unimportant to related parties. In this way, auditors are highly qualified and develop more in-depth knowledge about clients (Curtis & Turley, 2007; Kutum et al., 2015). Accordingly, it is not surprising that the research findings also point that the auditor's capacity has the strongest impact on the audit quality.

The application of information technology to audit activities is an indispensable trend, while businesses increasingly rely on computer systems to record, trace, and process transactions. This is reason why information technology has the second strongest influence on RBA implementation as well as audit quality. This result is in line with findings from studies of Nazmi et al. (2017), Van Buuren et al. (2014), and Tarek et al. (2017).

Interestingly, the competitiveness of audit firms has the strong influence on the performance of RBA but has the weak audit quality. The reason behind the positive relationship is that audit firms have competitive advantages such as large-scale, reputation as well as trained and provided adequate guidance documents to implement RBA (Phua et al., 2011). As a result, they should have ability to apply RBA more competently and thoroughly than other audit firms.

Audit fee is also considered as positive factors affecting RBA implementation. This study contradicts the view of Bell, Landsman and Shackelford (2001), and Curtis and Turley (2007) that the audit implementation by RBA does not reduce but instead increases audit fee. This explains why in Vietnam, RBA is not performed by small audit firm. Audit fee has no relationship with audit quality that is in line with studies of Choi et al. (2006), Mawutor et al. (2019), but is opposition with studies of Defond and Zhang (2014), Tobi et al. (2016), and Abdul-et al. (2017).

Client's risk has the strongest impact on RBA application but insignificant audit quality. In Vietnam, the majority of clients are small and medium-sized with poor internal management and control systems. Therefore, in most cases, the risk assessment results of clients are high and thus substantive testing remains or even increases. In other words, customer risk does not change the audit procedures (Le & Nguyen, 2020).

The research results also find a significant influence of RBA application on the audit quality. However, for optimal audit quality, it is necessary to consider ways of implementing RBA with different clients. Kutum et al. (2015) state that narrowing or expanding RBA depends on assessing business risks of clients with different sizes. According to Andersen (2006), small audit firms often audit small-scale clients, and require less complex audit procedures. In contrast, large firms are more likely to audit large-scale clients with more business risks, which require more complexly procedures. Robson, Humphrey, Khalifa and Jones (2007) realize that RBA are a good method but changes and adjustments are needed when auditing small customers.

Results of the study indicate that in order to carry out an audit with quality and efficiency by RBA, auditors and audit firms in Vietnam need to consider the following suggestions:

Firstly, improving the auditor's capacity. Unsurprisingly, audit capacity has always been identified by many studies as a factor that has an important influence on RBA application as well as audit quality. Therefore, the recommendation is first made for the auditors themselves. Especially in a current integrated economy and technology, besides efforts to learn knowledge and professional qualifications, auditors must strive to improve foreign languages ​​and information technology. On the other hand, the development of human resources is also greatly affected by the policies of audit firms in all stages: recruitment, training, management, and evaluation. Specifically, at the recruitment stage, policies must have a clear roadmap and focus on candidates with high levels of education and technology. At the training stage, it is necessary to provide programs regularly based on RBA commensurate with the modern information technology, and maintain the funding in both short and long term. Finally, KPIs performance measurement system is implemented at the stage of management and evaluation.

Secondly, applying RBA in information technology. Changes in procedures for processing, summarizing, and presenting information on financial statements in the context of information technology development require auditors to research and improve RBA. Moreover, audit firms need to invest in developing technology and equipping modern audit tools for auditors such as using high-tech audit software, sampling support software, analysis software, and security and storage software of customer data, etc. With the advantage of data processing speed, the software will help to improve the quality and efficiency of the audit, meet the requirements, and increase the trust level of clients.

Thirdly, enhancing competitiveness. Recognizing the importance of competitiveness for auditing activities, audit firms need to build a reasonable short-term and long-term business strategy, improve corporate governance capacity, gradually build brand, build corporate culture, and create reputation in the market. It is necessary to expand cooperation with foreign audit firms to gain experience and access advanced audit methods and technologies.

Fourthly, establishing a reasonable audit fee bracket. In order to enhance the openness, transparency and healthy business environment, it is necessary to have regulations on audit fee, which is publicized and quantified. From our viewpoint, the audit firms set the audit fee according to supply and demand relationship, but must ensure that it is calculated on the reasonable costs and professional ethics. At the same time, the registration of fee schedule with the Ministry of Finance, and VACPA help audit firms to manage and act as a basis for handling unfair competition.

Fifthly, adjusting RBA. According to Robson et al. (2007), and Khalifa et al. (2007), using RBA may not be beneficial for small-scale clients. Abdullatif and Al-Khadash (2010) conclude that business risk approach may be appropriate in principle, but the nature and weight of the risks evaluated have difference among environments. Similarly, a partial revision of RBA focus on clients of small and medium enterprises and the ability to tailor audits to the client's industry (Kutum et al., 2015). This study also shows that the competitiveness of different audit firms and the risk level of different customers also affect the implementation of RBA. From the above points, it can be seen that adjusting RBA is very necessary to suit the size of the audit firms and clients.

Finally, reducing job pressure. In audit activities, exposing to tangible and intangible pressures is unavoidable for auditors. However, the pressures can be controlled and reduced if auditors know how to arrange work in a scientific way, always upbeat and improve physical health. In addition, audit firms need to implement incentive and remuneration policies to increase motivation and satisfaction at workplace, create a friendly environment for auditors to exchange, learn, and share experiences.

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Le and Nguyen conceived the study and were responsible for the design and development of the data analysis. All authors were responsible for data collection, analysis, and interpretation. Le and Nguyen wrote the first draft. Le edited the article.

The authors declare no conflict of interest.