Google Scholar's Dramatic Coverage Improvement Five Years after Debut1

This article reports a 2010 empirical study using a 2005 study as a base to compare Google Scholar's coverage of scholarly journals with commercial services. Through random samples of eight databases, the author finds that, as of 2010, Google Scholar covers 98 to 100 percent of scholarly journals from both publicly accessible Web contents and from subscription-based databases that Google Scholar partners with. In 2005 the coverage of the same databases ranged from 30 to 88 percent. The author explores de-duplication of search results by Google Scholar and discusses its impacts on searches and library resources. With the dramatic improvement of Google Scholar, the uniqueness and effectiveness of subscription-based abstracts and indexes have dramatically changed.