After RefViz determines the vocabulary from the title and abstract/notes fields for a new set of references it assigns each term to one of three categories. Primary and Secondary status is based on how randomly the term occurs in each reference and the importance of the terms associated with it.
 

• Primary Keywords are mathematically determined by RefViz to be best for distinguishing and sorting references into groups. They are the terms that tend to be mentioned often in a subset of the references.
• Secondary Keywords are more evenly distributed across the reference set than Primary Keywords. They are less influential in creating groups but important for understanding relatedness among the Primary Keywords.
• Other Descriptive Terms are determined to be unimportant for distinguishing groups but can still be informative to the user for describing or understanding content.