Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:The exponent of the power law correlation is considered a measure of the magnitude of the Matthew Effect (Katz 1999; Ronda-Pupo and Katz 2016c; van Raan 2013) mathematically described in the following way.
Category: