## 3 Results
### Major Academic Branches of Design Research  
Major academic branches of design research are identified in this subsection. Firstly, the corpus of the LDA model consists of unique words obtained from the BASE table, which consists of 4893 unique words. To improve accuracy, a special stop word list just for academic articles in design research is created to remove the stop words. Next, we repeat the calculating of the perplexity of LDA model when the number of topic varies from 10-100, which aims to obtain an optimal topic set. Results are shown in Figure 1. When the number of topics is 30, the performance is the best. Thus, we apply LDA to remodel the preprocessed corpus by setting the number of topics to 30. Then, we get the topic distribution as the selected real-valued features for each article. Finally, we use K-means to perform classification with selected features and compare classification results, which is evaluated by SSE with different \(k\) values. Additionally, we compute inter-cluster distance with different \(k\) values, as listed in Table 1. In Figure 2, we can see that the value of SSE gets smaller as the value of \(k\) gradually increases from 2-8. The value of SSE achieves a relatively stable state when the value of \(k\) is greater than four. From Table 1, we can observe that the inter-cluster distances between Cluster 1 and Cluster 4, Cluster 2 and Cluster 3, Cluster 2 and Cluster 5, Cluster 3 and Cluster 5 are obviously smaller than other inter cluster distances when \(k\) is seven. We can merge Clusters 1, 4 and Clusters 2, 3, 5 into two clusters and obtain four clusters. The same analysis logically would apply to the circumstances when \(k\) is five and six.Thus, it is reasonable to classify all of the research articles into four clusters. Then, we calculate the four cluster centroids. According to top three topics in each cluster centroid in Table 2 and the top ten words of each topic in Table A3 of Appendix B, each cluster can be interpreted as an academic branch of design. Cluster 1 includes these words, \"interaction\", \"human-computer\", \"user\", \"interface\", etc. They reveal a discipline of design thatpays attention tosatisfying the needs and desires of the majority of people who will use the product. Therefore, Cluster 1 is called interaction design. Interaction design is about users' behaviors. It focuses on creating engaging interfaces with understanding how users and the web communicate with each other [14]. User experience is vital to all kinds of products and services. On the web, user experience becomes even more important [15]. The most frequently-used words in Cluster 2 are \"ergonomics\", \"musculoskeletal\", \"work\", \"physical\", \"back\", \"pain\", etc. These words are involved in harmonizing the functionality of tasks with the human requirements of those performing them. As a result, Cluster 2 is named ergonomic design. It is a branch of science drawing from physiology, engineering and psychology studies. It is often the most difficult variable to factor into the early stages of the design process. With poor ergonomic design, users may even be injured [16]. Ergonomic design is said to be human-centered design focusing on usability. It seeks to ensure that human restrictions and capabilities are met and supported by design options. These words, \"product\", \"design\", \"process\", \"theory\", etc., are contained in Cluster 3. The content of studies includes the process of creating a new product. These words also demonstrate the methods, strategies, research, analysis and management of design. To conclude, Cluster 2 belongs to product design. It presents an in-depth study of structured design processes and methods, which has many benefits in education and industry. On the industry side, a structured design process is mandatory to effectively decide what projects to bring to market, schedule this development pipeline in a changing uncertain world and efficiently create robust delightful products.