Methods: A cluster analysis was performed on the retrieved articles based on normalized
bibliographic coupling (i.e., based on shared references topically similar articles was placed in
mutually exclusive groups). The cluster analysis resulted in 19 clusters that were classified by
a subject expert from the field of SEP. Further, the labeled clusters were visualized as
research fronts along timelines subdivided into timeslices – 1985-1994; 1995-1999; 2000-
2004; 2005-2009 – showing the growth and decline of research topics within motivation
research in SEP. Direct citations between the research fronts was extracted and visualized in
order to explore information flow