Introduction

Bornmann and Marx (2013) proposed to complement the times cited perspective (the forward view in impact measurement) with the cited references perspective (the backward view; Leydesdorff and Amsterdamska 1990; Merton 1965; Zitt and Small 2008). Whereas the times cited perspective focusses on the later impact of a paper, the backward view is oriented towards the roots of a paper: which are the giants on which the research published in the paper stand (Merton 1965)? Based on the proposal of using the backwards view in impact measurement, Thor et al. (2016a) introduced the CRExplorer (see www.crexplorer.net)—a program that can be used to investigate the historical roots of various entities in science: single researchers, topics, fields, institutions, etc. (see also Thor et al. 2016b). Since its introduction, the program has been used, for instance, to investigate the roots of the field of citation analysis (Hou 2017) and the research landscape associated with Monoamine oxidases (Yeung et al. 2019).

Some month ago, the scientometrics community has lost an outstanding researcher. Judit Bar-Ilan (JB) was professor at the Department of Information Science (Bar-Ilan University, Israel) and received the Derek de Solla Price Memorial Medal in 2017 for her contributions to the fields of quantitative studies of science. As a search in Web of Science (WoS, Clarivate Analytics) using her ResearcherID (B-3452-2009) shows, she has published 117 papers between 1989 and 2018.Footnote 1 Most of the papers (87%) are in the core WoS category of scientometric research “Information Science Library Science”; nearly one quarter of the papers have been published in Scientometrics (Leydesdorff & Bornmann, in press). In this study, the results of a cited references analysis are presented investigating the historical roots of JB’s research in information science and scientometrics.

Methods

The 117 papers, which resulted from a search in WoS using JB’s ResearcherID (B-3452-2009), were downloaded as comma-separated values (CSV) and imported in CRExplorer. The dataset contained 4182 non-distinct cited references, which was reduced to 3301 distinct references. Sixty-three cited references were discarded from the set, because they did not have reference publication year information (which is necessary for conducting a cited references analysis). The minimum reference publication year is 1934 and the maximum 2018. Since cited references data are often misspelled, we used the disambiguation tools provided by CRExplorer to identify and unify the variants. This procedure reduced the set of cited references to n = 3295 which have been used for the statistical analysis.

Results

In this study, JB’s historical roots are defined as those publications cited by JB very frequently over many citing years. For identifying these publications, Thor et al. (2018) introduced the indicator N_TOP10; it is the number of citing years in which a cited publication (reference) belongs to the 10% most frequently referenced publications. The indicator assumes that the higher this number is, the more important or influential the cited publication (reference) had been for JB’s research. Note that the indicator is calculated based on only JB’s publications set. N_TOP10 is not connected to the well-known PPtop-10% indicator or excellence rate (Bornmann et al. 2012; Waltman et al. 2012). For these indicators, reference sets are generated which are not part of the publication set in question. For calculating the indicators for a single paper in a set, the 10% most frequently cited papers in the corresponding subject category (e.g., used in Scopus, Elsevier, or WoS) and publication year are determined (see Bornmann 2013).

Table 1 shows the title of the publications, which belong in at least five citing years to the 10% most frequently referenced publications by JB. The table includes also the abstracts of papers or short descriptions in case of books (when available). To support the interpretation of the historical root publications in Table 1, a co-occurrence network has been generated based on the keywords (author keywords and KeyWords Plus) from JB’s 117 papers. The network, which we produced with the program VOSviewer (see www.vosviewer.com), visualizes the topics of JB’s research (see Fig. 1). As the network results reveal, JB was active in various topics of information science and scientometrics: information retrieval (red, dark-blue nodes), internet—world-wide-web—research (blue, yellow nodes), information behaviour (dark-blue nodes), library metrics (bright-blue nodes), altmetrics (green nodes), and h index (green nodes).

Table 1 Historical roots of Judit Bar-Ilan’s work (cited publications with the highest number of citing years in which the publications belong to the 10% most frequently referenced publications)
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Fig. 1
figure 1

Co-occurrence network of keywords attributed to 117 papers published by Judit Bar-Ilan (based on minimum number of occurrences of keywords = 2)

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JB’s historical roots publications in Table 1 fit very well with JB’s research topics as visualized in Fig. 1: A seminal publication in information science is Saracevic (1975). Krippendorff (1980) and Salton (1989) deal with methods for analyzing the content of text documents (see also Salton 1970). These methods are relevant in research on information retrieval and information behaviour. Krippendorff (1980) is the central textbook for content analysis. Basic publications about the Internet—world-wide-web—research and search engines are Brin and Page (1998)—the paper grounding Google—and Bharat and Broder (1998), as well as Lawrence and Giles (1999). Lawrence and Giles (1999) is the locus classicus for research about search engines. The connection between the world-wide-web and the impact factor was made by Ingwersen (1998). This paper introduced the impact factor into webometrics. The h index has been introduced by Hirsch (2005) and Egghe (2006) proposed one of the most important h index variants, namely the g index (Bornmann and Daniel 2007; Bornmann et al. 2011). Pinski and Narin (1976) as well as Fagin et al. (2003) are methodologically oriented papers dealing with citation based influence measures and distance measures. Pinski and Narin (1976) is the classical paper about influence weights.

Discussion

JB was one of the most influential researchers in information science and scientometrics. She published more than 100 papers about different topics in both these fields. In this study, the historical roots of JB’s research have been investigated using the N_TOP10 indicator: publications were identified which have been very frequently cited by JB in several citing years. These publications are mostly seminal works in information science and scientometrics as well as methodologically oriented publications dealing with text or content analyses as well as influence or distance measures.

In recent years, historical roots of various units have been investigated in many studies based on cited references data (e.g., Ballandonne 2018; Barth et al. 2014). Advanced indicators such as N_TOP10 introduced recently by Thor et al. (2018) have been seldomly used in these studies, although the indicators have the advantage of supporting the identification of landmark publications referenced in publication sets. Since the analysis of JB’s publication set is a good example for the usefulness of the indicators, this study might encourage scientometricians to use them in future studies.