Web Citation Availability: A Follow-up Study

The researchers report on a study to examine the persistence of Web-based content. In 2002, a sample of 500 citations to Internet resources from articles published in library and information science journals in 1999 and 2000 were analyzed by citation characteristics and searched to determine cited content persistence, availability on the Web, and availability in the Internet Archive. Statistical analyses were conducted to identify citation characteristics associated with availability. The sample URLs were searched again between August 2005 and June 2006 to determine persistence, availability on the Web, and in the Internet Archive. As in the original study, the researchers cross-tabulated the results with URL characteristics and reviewed and analyzed journal instructions to authors on citing content on the Web. Findings included a decrease of 17.4 percent in persistence, and 8.2 percent in availability on the Web. When availability in the Internet Archives was factored in, the overall availability of Web content in the sample dropped from 89.2 percent to 80.6 percent. The statistical analysis confirmed the association between the likelihood that cited content will be found by future researchers and citation characteristics of content, domain, page type, and directory depth. The researchers also found an increase in the number of journals that provide instruction to authors on citing content on the Web

Methods for estimating the size of Google Scholar

The emergence of academic search engines (mainly Google Scholar and Microsoft Academic Search) that aspire to index the entirety of current academic knowledge has revived and increased interest in the size of the academic web. The main objective of this paper is to propose various methods to estimate the current size (number of indexed documents) of Google Scholar (May 2014) and to determine its validity, precision and reliability. To do this, we present, apply and discuss three empirical methods: an external estimate based on empirical studies of Google Scholar coverage, and two internal estimate methods based on direct, empty and absurd queries, respectively. The results, despite providing disparate values, place the estimated size of Google Scholar at around 160 to 165 million documents. However, all the methods show considerable limitations and uncertainties due to inconsistencies in the Google Scholar search functionalities.Comment: 22 pages, 4 figures and 6 tables. arXiv admin note: text overlap with arXiv:1407.623