Linda Bennett and Dimity Flanagan have published "Measuring the Impact of Digitized Theses: A Case Study from the London School of Economics" in Insights: the UKSG Journal.
Here's an excerpt:
This study tests the assertion that the online dissemination of theses has a positive impact on the research profile of the institution and sets out to gain a greater understanding of how digital theses fit into the scholarly resources landscape. The year-long study combined primary and secondary research and was undertaken with the London School of Economics, based on its programme of theses digitization. The paper outlines the types of metrics an institution may use to measure the impact of its corpus of digitized dissertations and examines how these metrics may be generated. Findings included: a higher volume of theses attracts more traffic; Google's strong indexing capabilities make it the most frequently used tool for discovery of digital theses; primary conclusions are that there is little correlation between downloads and citations of digitized theses; having a digital thesis collection enhances the reputation of the institution; although they recognize that digital theses are a valuable research tool, postgraduates and academics widely believe that making them available affects future publication opportunities; building and maintaining a digital thesis collection makes considerable 'hidden' work for librarians in terms of training about copyright and permissions. Some conclusions: better statistics are needed, especially of citations; institutions need to promote digital thesis collections better; more work needs to be done on whether digitizing theses impairs authors' chances of traditional publication and on how digital theses affect and are affected by the open access movement.