Philip M. Davis, Studies on access: a review, preprint, self-archived December 20, 2009. Abstract:

A review of the empirical literature on access to scholarly information. This review focuses on surveys of authors, article download and citation analysis.

From the article:

… In reviewing the literature, there is surprising consistency in the conclusions of these
studies: access to the published literature is improving, and those who generate knowledge view
access issues as largely unimportant. We should emphasize the phrase “those who generate
knowledge,” since there has been very little work on the dissemination of scientific information
to those who use – but do not contribute to – the literature (i.e. teachers, medical practitioners, industrial researchers, and the lay public).

Moreover, most studies have focused on access to the formal, published literature and
assume that access is provided either directly from the publisher or through a library
intermediary. We should not ignore the many informal ways academics share documents among
informal networks of peers. Lastly, we should understand that most of the surveys and
interviews cited below were conducted prior to the recent economic downturn, which have
resulted in significant material reductions in major academic libraries. …