The Pearson correlation coefficients between items (papers) were calculated and
used as the basis for PFNeT scaling [21, 22, 23]. The value of Pearson correlation
coefficient falls between the range -1 and 1. The coefficient approaches to one when
two items correlate completely. Items that closely relate, i.e., are highly correlated,
and should be placed closely together spatially.
The nodes located close to the center of a PFNeT graph represents papers
contributed to a fundamental concept, which are frequently referred by other
peripheral literature that are positioned in outer branches. The distance between items
is inversely propositional to the correlation coefficient, which maps less correlated
items apart and highly correlated items spatially adjacent [8, 13]