User Experience: A Bibliometric Review of the Literature

User experience is a well-discussed topic in the field of human–computer interaction. To describe the status of research on this topic, a bibliometric analysis of publications concerning user experience from 2011 to 2021 was conducted using the Web of Science database. The main functions of Derwent Data Analyzer software include data cleaning, mining, and visualization. The historical trends of the year, leading countries, leading institutions, major contributors, and leading research fields and journals were investigated, and a keyword analysis of the highly cited literature was performed. The key findings are as follows. The United States, China, and Britain are the three most productive countries. Tsinghua University in China is the most productive organization, and Sungkyunkwan University in South Korea has the highest average citations per publication. User experience has attracted the attention of numerous scholars in 204 research fields, and computer science information systems is the main field. “Usability,” “virtual reality,” “human–computer interaction,” and “augmented reality” are the most used keywords. A recent trend is the focus on molecular biology.

The concept of UX was put forward by Donald Norman, the world's first UX designer appointed by Apple in the 1990s. He believes that UX should meet the customers' needs, and a product's design should be simple and generous, such that it makes users happy with the product and brings them additional surprises [34]. With the increasing interest in this area, the content of UX research continues to expand, and the framework continues to improve. Alben [35] believes that ''experience'' refers to all aspects of people's use of interactive products: the feeling of the product in their hands, their understanding of the working principle of the product, their feeling when using the product, how the product meets their purpose, and the fit of the product with the whole environment in which they use the product. Nielsen et al. [36] believed that UX includes all interaction factors between end users and enterprises, their products, and services. Garret [37] put forward a UX model in the elements of UX: a user-centered design (UCD) for the web composed of ''elements'' existing in the ''plane'' of the development process. Each website develops at five levels from the bottom to the top: strategy, scope, structure, framework, and surface. Hassenzahl and Tractinsky [1] highlighted that UX is the result of the user's internal state (tendency, expectation, demand, motivation, emotion, etc.), the features of the design system (e.g., complexity, purpose, availability, functionality, etc.) and the interaction environment (or environment; e.g., organizational or social environment, significance of activities, voluntary use, etc.). Partala and Kallinen [38] emphasize that the main structure of UX should include experience emotion, satisfaction of psychological needs, and contextual factors. The UX model widely used at present is mainly the UX cellular model proposed by Peter Morville [39], [40].
At present, some reviews have summarized the research results concerning UX, but they merely offer a review of the development of UX in a specific field and lack a comprehensive analysis of UX in various fields. For example, Kim et al. [62] believe that the virtual reality (VR) system presents extensive interaction with users, and new types of interactions are constantly being developed. Therefore, it is necessary to keep eyes on the UX of the VR system. To determine the current research status and future research direction, the UX research of VR has been systematically reviewed.
Hornbaek and Hertzum [63] reviewed papers on the intersection of the technology acceptance and UX models to explore the experience component of HCI. In order to evaluate the user satisfaction of different types of computer games, Phan et al. [64] designed and developed a scale called ''Game User Experience Satisfaction Scale'' Brajnik and Gabrielli [65] reviewed studies on how online display advertising affects website usability and UX quality in the past decade. Clearly, the current overview in the field of UX is not comprehensive enough to systematically describe the research situation of UX from a global perspective, nor to judge the research hotspots and trends. As the first survey using bibliometrics on the topic of UX, this paper systematically summarizes the current status of UX research worldwide, focuses on the research hotspots, and predicts future research directions through a keyword analysis.
Bibliometrics is commonly known as statistical document analysis, in which statistical methods are applied to make a simple statistical analysis of the characteristics of relevant documents containing strategic intelligence, and data are analyzed to describe or explain the data characteristics and the change rules of the documents, to achieve the purpose of a strategic intelligence research. Many fields of research use bibliometrics to explore the effect of papers in specific research areas and to determine the influence of specific research areas or researchers [66]. It is widely used in research and evaluation in many fields [67] such as humanities [68], management [69], social sciences [70], tourism [71], economics [72], biomedicine [73], information technology [74], chemical engineering [75], architecture [76], psychology [77], machinery [78], education [79], and artificial intelligence [80].

II. MATERIALS AND METHODS
Bibliometrics is an interdisciplinary science that quantitatively analyzes all knowledge carriers using mathematical and statistical methods. Unlike a systematic review of papers, bibliometrics allows the analysis of numerous papers to show the overall research situation of a given topic, such as UX, based on the literature. This study analyzes ''user experience-related'' literature published between 2011 and 2021. The data were obtained from the core database of Web of Science (WoS) as of December 1, 2021. The search field was the subject, specifically, ''user experience'' or ''user's experience,'' and the document type was ''article'' or ''review.'' Finally, 6,748 articles were collected from Science Citation Index (SCI) and Social Sciences Citation Index (SSCI). The annual output analysis showed that the number of articles before 2011 was small and unstable. Therefore, we limited this study's scope to 5,842 articles published between 2011 and 2021. We used Derwent Data Analyzer (DDA10.0 build 27330, Norcross search technology company, Georgia, USA)-a statistical analysis tool for data cleaning, data mining, and data visualization-to process and analyze data extracted from 5,842 articles and tables. All articles related to UX from 2011 to 2021 were evaluated in the following aspects: countries, international cooperation, institutions, research fields, journals, authors, author keywords, and most frequently cited paper for each year.

III. RESULTS
From 2011 to 2021, 107 countries or regions published 5,842 articles regarding ''user experience.'' Of the 5,842 papers, 73 were highly cited papers on essential science indicators(ESI), and three were prominent papers on ESI. The annual growth trend of the research on UX is shown in Fig. 1. The number of publications per year increased from 144 (2011) to 998 (2021), nearly sevenfold. More than three quarters of the literature was published in the past six years (2016-2021). This finding shows that UX is a considerable topic in the field of HCI, attracting the attention of scholars worldwide.

A. CONTRIBUTION OF LEADING COUNTRIES OR REGIONS
The top 20 countries with the most contributions from UX papers are shown in Fig. 1, and their proportions are shown in Fig. 2. Among the 20 countries or regions with the highest productivity, 11 are from Europe; 3 from the VOLUME 11, 2023 Americas; 5 from Asia and 1 from Oceania. The United States is the most productive (1,366 articles), followed by China (1,343) and Britain (663). China includes Taiwan. Britain includes England, Wales, Scotland, and Northern Ireland. Japan has the highest average citations per publication (ACPP; 102.39), indicating that its influence in this field cannot be ignored. Among the literature of the top 20 countries, there are a lot of references to international cooperation, especially for Switzerland (87.76%), Singapore (81.37%), and Norway (65.31%). Therefore, scholars have intensively participated and cooperated in the knowledge exchange regarding UX. Although China has numerous publications, its ACPP is low at 12.43, probably because of language barriers and the quality of incremental articles. The cooperation among the top 20 countries is shown in Fig. 3. The more articles in each country, the larger the nodes. The connection between the nodes is representative of cooperation among these countries, and its width represents the intensity of such cooperation. The number of cooperative countries (NCC) values in Table 1 prove that the United States is the most active country in terms of cooperation. It has cooperated with 70 countries or regions, especially China, South Korea, the United Kingdom, and Canada; followed by Britain (69) and France (50). In addition to close cooperation with the United States, China also has strong cooperation with Australia.      network, having cooperated with 11 institutions. Huazhong University of Science and Technology has cooperated with nine institutions, and Tsinghua University has cooperated with eight institutions. These results suggest that institutions from China often have a good foundation for cooperation. Sungkyunkwan University shows the least cooperation, having cooperated only with Nanyang Technology University in Singapore. Most of the cooperation between institutions is not limited to domestic contacts; all have the experience of cooperating with foreign institutions, indicating the global nature of UX research.

C. CONTRIBUTION OF LEADING RESEARCH AREAS
It is generally accepted that UX is a topic relevant to multiple disciplines. Based on the number of articles, table 3 shows the top 20 most popular research areas for UX. Computer science information systems ranks first with 1,348 articles, followed by electrical engineering and electronics (1,179) and telecommunications (1001). These are the main areas of UX research, accounting for 60.38% of the total published articles. As shown in Fig. 6, the number of articles published in the top 20 fields generally rises yearly, indicating that the topic of UX is increasingly attracting scholars' attention. The aforementioned three areas are also the most closely linked, as shown in Fig. 7. Next is computer science information systems, which is closely related to computer science software engineering and computer science theory methods. Meanwhile, the area of psychology has the highest ACPP value, which indicates that many theories and models of UX are from this field, and many psychology-related methods are used in the UX evaluation process.

D. CONTRIBUTION OF LEADING JOURNALS
Between 2011 and 2021, 5,842 articles in the field of UX were accepted by 1,462 journals. As shown in Table 4, 1EEE Access leads with 200 articles on UX, followed by Multimedia Tools and Applications (107), Sensors (106), International Journal of Human-Compute Studies (87 articles), and International Journal of Human-Computer Interaction (85 articles). The 20 journals listed in Table 4    publication of the top 20 journals, we present a bubble chart of the top 20 productivity journals (Fig. 8). Articles on the topic of UX have been published since 2011. However, from 2016, numerous articles on this topic have been published in journals represented by IEEE Access, suggesting that this topic has received great attention from academia and that product development, website design, and other works have prioritized the users' perspective.    Li, Chunlin; Liu, Jun; Luo, Youlong; Li, Yong; Chen, Min; Thomaschewski, Joerg; and between Schrepp and Martin (Fig. 9). Nine of the top 20 authors have not collaborated with other authors. The publications of the top 20 authors accounted for only 4.02% of the total, which means that many researchers are involved in the field of UX, contributing to 5,842 articles. Such a large research population also promotes the field of UX to achieve breakthroughs in the future.

F. RESEARCH HOTSPOTS AND TRENDS
The author's keywords contain key information about the current research status and hotspots. These keywords have been proven to play an important role in the analysis of future development trends [81], [82], [83]. We analyzed 14,660 keywords in 5,842 articles, of which 1,606 were used more than 3 times. Note that some articles without keywords may be excluded from the statistics. The top 20 keywords VOLUME 11, 2023 sorted by year are shown in Fig. 10. Keywords with similar meanings are classified into the same item after DDA processing. The three-dimensional development trend of the field is shown in a bubble chart. The chart tracks the research frontier by using bubble size as a third dimension [84]. The number in the bubble indicates the frequency of the keyword for a specific year. Ranking second after the search term ''user experience'' is ''usability,'' which is considered part of UX (260), followed by ''virtual reality'' (209), ''human-computer interaction'' (178), ''augmented reality'' (128), ''mhealth'' (111), ''mobile app'' (98), ''Internet of Things (97), ''machine learning'' (91), and ''quality of experience'' (86), which correspondingly rank third to tenth.
The top 20 keywords are divided into the following categories: 1) Terms related to UX-This includes ''user experience,'' ''usability,'' ''human-computer interaction,'' ''quality of experience,'' ''user interface,'' and ''user-centered design.'' UX is an important module in the field of HCI [1], [85], [86], and usability is an important part of UX [87], [88]; thus, the frequency of these two keywords is very high. A large part of UX research focuses on usability. For example, Hoehle and Venkatesh [89] proposed a conceptualization and survey tool for mobile application availability. To understand the effectiveness and availability of e-learning systems, Harrati et al. [90] discussed how teachers can interact with the e-learning environment based on a predefined task model. Some researches focus on quality of experience (QoE) or quality of service (QoS) in UX. Hobfeld et al. [91] discussed the technical challenges in transferring services to cloud computing and how this transformation affects QoE and QoE management. Yin et al. [92] emphasized the importance of QoS in internet video applications and developed a principled control theory model to infer a wide range of policies. Research in the field of computer systems often evaluates UX from the perspective of user interface (UI). Hussain et al. [93] believe that many methods affect the UX by providing individualized services in the form of adaptive UI. Shahzad [94] discussed the strategy of introducing ontology into different user interface layers according to UX elements. Kim et al. [95] studied and investigated the degree of user interface reflection, that is, the degree of interaction between the user's body and the game, and how this influence the UX, game behavior, and purpose of behavior change. In addition, more studies have focused on emotional factors other than usability in the UX. Park et al. [96] believe that emotion is an important aspect of UX. To design a UI for positive emotional experience, we need to consider the emotional quality of the UI carefully. Gil et al. [97] pointed out that as a means of improving the UX, emotion-awareness applications are receiving widespread attention.
2) Relevant stages of UX-This includes design and evaluation. Previous UX studies often focused on the evaluation stage [98], [99], [100]. Now, studies increasingly begin to consider UX from the design stage [101], [102], which coincides with the concept of UCD. At present, research on product design and development increasingly use the keyword ''user-centered design,'' emphasizing the idea of UX throughout the whole process of product design. Kübler et al. [103] applied UCD in the development of brain computer interfaces (BCI) to bridge the gap when providing users with BCI for controlling applications. To help realize UCD, Yamazaki and Furuta [104] developed a tool for UX design and evaluated the tool by prototyping experiments. Maher et al. [105] designed and developed tools that can be used for the habitual practice of patients and caregivers in the inpatient environment according to the concept of UCD. Triberti et al. [106] discussed the necessity of integrating emotional analysis into UCD. The research on UX is gradually developing toward the full cycle.
3) Different scenarios and domains of UX-This includes virtual reality, augmented reality, mMealth, mobile app, Internet of Things, cloud computing, eHealth, telemedicine, smart phone, and recommender system. Keywords in different scenarios and fields account for a large proportion, suggesting that UX is a popular research topic applied in many fields, and UX evaluation in many new scenarios has emerged [107], [108], [109]. 4) Related technologies of UX-This includes machine learning and eye tracking. At present, the technology of evaluating UX shows a multimethod and multi-index trend, combining subjectivity and objectivity, which is specifically reflected in the expansion of machine learning and the application of eye movement technology. In the past, questionnaire and interview methods were mostly used to conduct feedback surveys on a narrow range of users, with a small amount of data and strong subjectivity. These problems disappeared after machine learning was applied to UX evaluation [110], [111]. In addition, many studies evaluate the UX in machine learning models [112], [113], [114]. Eye-tracking technology also ensures the objectivity of data [115], [116], [117].

G. ANALYSIS OF THE MOST CITED PAPERS
Although the citation of articles is influenced by many factors, it remains a widely used method to assess the quality of an article. The most cited articles from 2011 to 2021 are shown in Table 6. The most cited article was written by Sudhir et al. [118], which was published in Molecular Biology and Evolution, ranking first with 10,559 citations and simultaneously topping the total citation per year (TCY).
If a paper is co-authored by scholars from different countries, the paper is defined as a product of international cooperation [119]. Among the 11 most cited articles, 7 were co-authored by people from more than one country, indicating the importance of transnational cooperation to the literature in this field. The 10 articles include authors from the United States, indicating the dominant position of the United States in this field. Notably the most cited literature each year involves virtual reality, biology, communication engineering, the Internet of Things, and other fields, suggesting that UX has the characteristics of interdisciplinary integration.  In 2014, Andrews et al. [6] introduced the similarities and differences between 5G and the previous four generations of cellular technology. 5G combines air interface and spectrum with long term evolution (LTE) and WiFi to provide universal high-speed coverage and a seamless UX [6]. The authors started the research and discussion on 5G in the following years. In 2016, Agiwal et al. [120] published an article, once again garnering the highest number of citations for that year. This article reviews 5G in detail after two years of development, and focuses on the new QoS, QoE, and SON functions related to 5G evolution, to understand the improvement of UX.
Among the 11 most cited articles each year, 7 are in the field of biochemistry and molecular biology, which shows that scholars in this field attach great importance to UX. Chen et al. [121] discussed the optical modification of laser scanning microscope for measurement and pointed out the calibration time required according to the UX level. Thorvaldsdottir et al. [12] introduced the integrated genomics viewer in detail, pointing out that it provides a smooth and better UX at all levels of genome resolution. In an article published in 2015, titled ''UniProt: A hub for protein information,'' Bateman et al. [122] used the UX design process to design a new website about UniPort, to determine which proteins have the best characteristics and provide the most information for comparative analysis. The two most cited articles in 2018 and 2020 both introduced the molecular evolutionary genetic analysis (MEGA) software. Sudhir et al. [118] reported a transformation of MEGA to achieve cross-platform use on Microsoft Windows and Linux operating systems and provide a unified cross-platform UX. Stecher et al. [123] focused on the new version of the macOS of the MEGA software, which eliminates the virtualization and simulation programs required for using Mega on Apple computers as before, to provide a UX consistent with that on Windows and Linux.
The most cited article in 2017 introduced the integration and application of edge computing and the IoT, to provide a better UX and the resilience of services in case of failure [124].

IV. DISCUSSION
Although UX is a topic that has been researched for 30 years, with the rapid growth of computer network, artificial intelligence, and other technologies, as well as the deepening of the user-centered concept, this topic continues to receive research attention. From 2011 to 2021, 107 countries and regions paid attention to UX research and published a total of 5,842 articles. Except for China, India, and Brazil, the top 20 countries are all developed countries. A possible reason is that highincome countries pay more attention to the personal experience of users. In terms of the number of publications, China and the United States are far ahead, with little difference between them. The cooperation between the two countries is also the closest. However, a gap continues between the total cited number of Chinese literature and the h-index compared with the United States, which is also reflected in terms of institutions. Institutions from China account for eight of the top 20 most productive institutions, but the ACPP and Hindex of the literature need to be improved, indicating that Chinese scholars need to conduct more in-depth research in the field of UX.
The development of UX puts forward higher requirements for computer science, electrical and electronics, communication engineering, and many other fields. These areas in turn promote the development of UX. This is reflected in the publication volume of journals. IEEE Access, which ranks first in publication volume, is a journal that collects articles in the whole field, and Multimedia Tools and Applications, which ranks second, covers computer systems and engineering electronics, while the third-ranked Sensors focuses on engineering technology. Different fields have different research paradigms for UX. For example, UX in computer science mainly focuses on human-computer interaction of websites and systems [125], [126]. In the aspect of industrial design, the user centered idea runs through the design, emphasizing users' positive experience of products [127], [128]. In addition to the theoretical background of UX measurement [129], [130], model framework [131], and measurement methods and tools [132], the emotional aspects (psychology) of UX are also explored, such as privacy acceptance and satisfaction [133], [134].
Virtual reality technology and augmented reality technology are popular technologies nowadays, which are widely used in many fields [135]. Although the development of VR/AR provides many new possibilities for content design, the design's immaturity poses severe challenges to practitioners. The design of VR/AR also needs feedback from the UX perspective to verify whether it is feasible. Simultaneously, with the improvement of users' requirements for content quality, whether there is a good experience determines whether users will continue to use the VR/AR product. The UX of VR/AR involves many aspects such as the VR/AR equipment itself [136], [137], education [65], [138], medical treatment [18], [139], industry [140], [141], and so on. Some scholars have discussed how UX in VR/AR can be evaluated. For example, Kuliga et al. [142] have investigated whether UX in real buildings and virtual buildings is consistent. Rebelo et al. [143] discussed how to conduct UX assessment in a VR environment to overcome the limitations of UX assessment in the laboratory.
With the innovation of mobile technology and the growing number of smartphone and tablet users, mobile applications are becoming increasingly popular. Good UX can improve customer satisfaction and loyalty. Therefore, UX of mobile applications has become critical in academia and various industries [144]. Compared with the traditional UX evaluation method, mobile applications can obtain data through the comments of the app store [86], [145], [146]. Compared with the amount of data obtained in previous UX studies, the amount of user feedback obtained in this manner has greatly increased, which is also the trend of future research.

V. CONCLUSION
In this study, we analyzed the UX research literature published from 2011 to 2021 using bibliometrics and DDA software. According to our analysis, scholars in North America, Europe, and Asia actively conduct research on UX. Among them, the United States is the leader, followed by China and Britain. China and the United States are the two countries that cooperate most closely. Japan has the highest ACPP. Tsinghua University, the Chinese Academy of Sciences, and Beijing University of Posts and Telecommunications in China are the three institutions with the highest output, while Sungkyunkwan University in South Korea has the highest ACPP.
Shin, Dong-Hee; Park, Jaehyun; and Thomaschewski, Joerg are the three most prolific authors. Shin, Dong-Hee also has the highest h-index, while Chen, Min has the highest ACPP value. Although the top 20 authors have great influence, many other researchers work in this field, accounting for 95.98%. In addition, ten of the most cited articles in the past 11 years involve American scholars, which, once again, reflects the leading position of the United States in this field. The keywords ''virtual reality,'' ''augmented reality,'' ''human-computer interaction'' and ''mhealth'' are the most common. In the past decade, the research on UX has been conducted in different fields and disciplines, and a series of discussions have been carried out on how to understand UX and how to improve it. In recent years, virtual reality, augmented reality, and molecular biology are the most popular areas of research concerning UX.
This study can help potential scholars better understand the research status in the field of UX worldwide and provide ideas and information for future research.