“…The source words can come from keyword lists, titles, abstracts, or other publication data fields. In past studies, researchers have used a variety of techniques to create clusters from bibliometric data, including factor analysis [WHITE & MCCAIN, 1998], principal component analysis [SALVADOR & LOPEZ-MARTINEZ, 2000], and hierarchical clustering [BORNER& AL., 2003;COULTER & AL., 1998;BAUIN & AL., 1991;WHITE & MCCAIN, 1998]. …”