The analyzed papers include over 26,500 unique references, of which only 82 are cited by more than 20 papers in our database. When analyzing the co-citation network using the network analysis (Figure \ref{494252}), several references clearly emerged as central in the network highlighting their importance in the field. For example, several references cited many times together in the analyzed hierarchical modeling papers are \citealp{MacKenzie_2002}\citealp{RN743}\citealp{2004}\citealp{RN744}\citealp{Fiske_2011}\citealp{MacKenzie_2003}, \citealp{Royle_2004} and \citealp{Dorazio_2005}. Furthermore, the popular references (references with a high normalized degree, i.e., number of links with other references in the database) and high betweenness (citations that frequently create the shortest path between different reference lists otherwise disconnected) reveal a list of 20 references that can be considered as very important by the authors publishing in this field (Figure \ref{585299}).