Page - (000250) - in Knowledge and Networks

246 bution of frequencies for each journal pair. We could then evaluate the z-score for each observed journal pair relative to what was expected by chance: z obs= ( exp)/- σ Where obs is the observed frequency of the journal pair in the actual WOS while exp is the mean and σ is the standard deviation of the number of journal pairs obtained from the 10 randomized simulations of the paper-to-paper citation network. Finally, returning to categorizing a paper’s prior work regarding novelty and con- ventionality, we could then assign a z-score to each of the journal pairs in that paper’s reference list. Each paper thus had a distribution of journal pairings, where any given pairing could be more or less common compared to chance. To summa- rize the information in this distribution, we took two primary summary statistics: (i) The median z-score for that paper. (ii) The 10th percentile z-score for that paper. Fig. 12.1 Paper pairs and journal pairs. This figure presents a stylized example of how paper pairs and journal pairs are drawn from the network structure of citations. In panel A, the circular nodes represent papers; the directed links exist when the top paper cites the bottom four papers. In panel B, the circular nodes represent papers, and the undirected co-citation links between papers are shown in black. A co-citation exists between each pair of papers that occurs in the reference list of the focal paper. Here, there are 4 references and therefore 6 (i.e., 4 choose 2) co-citation links. In panel C, paper nodes are grouped by journal; the shaded ovals represent the three journals in which each of the cited papers is published. Finally, in panel D, the co-citation links between papers are mapped to the journal level, and the black links represent journal co-citations. Note that the total number of paper-to-paper co-citation links (6) is preserved at the journal co-citation level (From Uzzi et al. (2013b, p. 10). Copyright 2013 by Science. Adapted with permission from the authors and Science) S. Mukherjee et al.