# A Bibliometric Overview of Twitter-Related Studies Indexed in Web of Science
## 4 Results and Discussion
### Science Mapping
#### 4.2.2. Thematic Analysis  
For the analysis of topic evolution across time, a set of time slices is made. According to the Annual Scientific Production, we take three periods to segment the whole Twitter-related scientific development process into three phases: Initial period is from 2006 to 2012: in this period, the publication number is not so much as later years, but RGR is relatively high, DT kept steadily with mild changes. The developing period is from 2013 to 2016; in this period the number of publications increased rapidly, RGR slowed down while DT started to slightly grow. The advanced period is from 2017 to 2020; in this period the number of publications arrived peak, while RGR kept turning down, DT grew immensely. Figure 6 presents the thematic maps of the three periods, each of the circles represents a cluster and the size of the circle represents the size of the cluster (the number of included terms/keywords). There are fewer clusters in developing and advanced period than the initial period, which implies that there are fewer research topics in last years than the first years. Figure 6: Thematic maps of the three periods. (**A**) Initial period, (**B**) developing period and (**C**) advanced period. For the initial period (2006-2012), there are two clusters on the first quadrant with high centrality and density, \"marketing, online, google\" and \"social-web, wikipedia\", these clusters focused on Twitter and other well-known website and marketing, are the motor research themes of this period. The third quadrant mainly consists of three clusters, \"innovation\", \"crowd-sourcing\" and \"advertising\", all these three clusters can be considered as specific research topics for business subject, they are the highly developed and isolated themes of 2006-2012. While Twitter was a newly emerged social media in that time, business related topics revealed a high centrality in the initial period, they have been hugely developed in the first years since the foundation of Twitter. \"Democracy, arab-spring\" and \"design, event-detection, mobile\" are the emerging or declining themes, they are independent from each other, \"democracy, arab-spring\" corresponds to 2010 arab-spring revolution, \"design, event-detection, mobile\" might related to the studies about smartphone and mobile application, such new electronic device and software also appeared after 2010, there are publications such as \"Tweeting with the telly on! Mobile phones as second screen for TV\", \"Mobile apps: innovative technology for globalization and inclusion of developing countries\" can prove our assumption. It is more reasonable to classify these two clusters as emerging themes, compared to the foundation of Twitter (2006), from 2006 to 2012, such political events and technological innovation occurred in 2010 was even newer. \"Social-networking-site, linkedin, student\", \"social-media, microblogging, microblog\", \"social-network, web, facebook\" are the three clusters that belong to basic and transversal themes; they are mainly focused on other virtual social networks, comparative studies about Twitter and other similar platforms are another important research line in the initial period. However, based on the previous argument, the \"social-networking-site, linkedin, student\" cluster may also refer to the studies of human resources, online employment and education, there are publications like \"Using facebook, linkedin and Twitter for your career\", \"Friend or foe? The promise and pitfalls of using social networking sites for HR decisions\", \"Comparative survey of students' behavior on social networks (in Czech perspective)\" can prove our assumption. For the developing period (2013-2016), in general, topics related to business, mobile and arab-spring disappeared from the map, contrarily, computer science related nouns emerged in this period (e.g., algorithm, sentiment-analysis). Cross-platform comparative studies (\"social-media, facebook, internet\" cluster) moved from basic and transversal themes to motor themes.