Paths of Discovery: Comparing the Search Effectiveness of EBSCO Discovery Service, Summon, Google Scholar, and Conventional Library Resources.  Andrew D. Asher, Lynda M. Duke, and Suzanne Wilson. Coll. res. libr. September 2013 74:464-488.

“In 2011, researchers at Bucknell University and Illinois Wesleyan University compared the search efficacy of Serial Solutions Summon, EBSCO Discovery Service, Google Scholar, and conventional library databases. Using a mixed-methods approach, qualitative and quantitative data were gathered on students’ usage of these tools. Regardless of the search system, students exhibited a marked inability to effectively evaluate sources and a heavy reliance on default search settings. This article describes these results and makes recommendations for libraries considering these tools.”