## 4 Experiments
### A Case Study  
We conduct a case study on a target article (PubMed ID: 22707478 [38]) to further analyze the contribution of BCCCC, as seen in Figure 4. Based on the curation by CTD experts, the article focuses on associations of the chemical Bisphenol A with several genes such as ESRRG and ESR1 (i.e., associations <Bisphenol A, ESRRG> and <Bisphenol A, ESR1>). Bisphenol A is a synthetic compound that exhibits estrogen-mimicking properties. ESRRG (Estrogen Related Receptor Gamma) and ESR1 are two genes that respectively encode estrogen receptor-related receptors and Estrogen Receptor \(\alpha\) (ER\(\alpha\)). As a test article, article 18197296 [39] focuses on associations of the gene ESRRG with two chemicals including Bisphenol A (i.e., association <Bisphenol A, ESRRG>). This article is thus highly related to the target article (i.e., article 22707478 noted above), with the association <Bisphenol A, ESRRG> as their common research focus. Another test article is article 17850458 [40]. It focuses on associations of the chemical Estradiol with two genes ESR1 and ESR2 (i.e., associations <Estradiol, ESR1> and <Estradiol, ESR2>). Estradiol is a female sex hormone, while ESR2 is a gene that encodes Estrogen Receptor \(\beta\) (ER\(\beta\)). Therefore, although this article and the target article (22707478) have a common focus on the gene ESR1, they are _not_ highly related, as they actually focus on associations of ESR1 with _different_ chemicals (article 17850458 focuses on <Estradiol, ESR1>, but article 22707478 focuses on <Bisphenol A, ESR1>). Therefore, given article 22707478 as a target, article 18197296 is a highly related article, while article 17850458 is a less related article, as seen in Figure 4, and hence the former should be ranked higher than the latter. However, better baselines in the experiment fail to do so. They prefer article 17850458 to article 18197296 by ranking article 17850458 at the top three positions (DBC: top position; IBS: top position; BM25 ref: the 3 rd position; BC: the 3 rd position), but article 18197296 after the 11 th position. BCCCC successfully ranks the less related article at the lower position (the 7 th position) and the highly related article at the top position. We further analyze why BCCCC can rank the highly related article (i.e., article 18197296) at the top position for the target article (i.e., article 22707478). References cited by the two articles tend to have low text-based similarities in their titles (i.e., _TextSimprof_ is low), while many of these references have high citation-based similarities (i.e., _CitationSimprof_ is high). Only 15 pairs of the references have TextSimref 0.15, but 67 pairs of the references have CitationSimref 0.5. This is the reason why BCCCC can successfully rank article 18197296 high, but the baselines cannot. Figure 5 shows an example to illustrate the analysis. Article 22707478 (the target article) and article 18197296 (the highly related article) respectively cite articles 22101008 [41] and 12185669 [42] as references (see \(r_{1}\) and \(r_{2}\) in Table 2). The two references share no terms in their titles, and hence their text-based similarity (_TextSimprof_) is 0. On the other hand, although the two references are _not_ cocited by any articles, they are cited by _different_ articles in the same categories (see categories \(c_{1}\) to \(c_{3}\) in Figure 5). Therefore, by category-based cocitation, _CitationSimprof_ between the two references is high (0.647), indicating that the two references may be highly related, and hence BCCCC similarity between the target article and the highly related article can be increased. Figure 4: A case study to analyze how BCCCC successfully ranks a highly related article (article 18197296) higher than a less related article (article 17850458) for a given target article (article 22707478). We then analyze why BCCCC can rank the less related article (i.e., article 17850458) at a lower position (the 7 th position) for the target article (i.e., article 22707478).