This post includes a few small points of clarification in response to one point made in a recent letter by publishers to JISC, as follows:
"It is misleading not to explain to UK universities that the hypothesized “savings” require the rest of the world to support open access. The rest of the world accounts for 93.4% of published articles, only 1-2% of which are ‘gold’ and only 7% of which are ‘green’ today. Until the rest of the world follows UK universities, which would likely take decades based on the current pace of change, UK universities would pay significantly more with no extra benefit". from: letter to M. Read, JISC, from G. Taylor (the Publishers Association), I. Russell (ALPSP) and M. Mabe (STM), March 15, 2010, downloadable from here.
The Houghton report does not assume that the whole world needs to move to open access; the cost savings quoted are based on a scenario of a unilateral move to OA by the UK. While this makes sense for a UK-based economic analysis (the UK Higher Education system cannot require changes elsewhere), the open access movement is actually global in scope. One way to view the UK in the global picture is to look at the Directory of Open Access Journals' statistics by country. Here we see that 406 OA journals are published in the UK, just under 10% of the total number of OA journals listed in DOAJ. The long list of countries publishing OA journals illustrates the global diversity of the movement.
Similarly, the global diversity of the open access repository (green) movement can be easily seen by a search of OpenDOAR "by country". Open access repositories are spread throughout Africa, Australia, North, South, and Central America, as well as Europe.
A global analysis of cost savings from a full switch to open access is likely to show far greater savings for the UK (and every other country) than a unilateral shift. My own macro-level estimate of library savings from a full shift to open access at top-quality PLoS rates is about 2.5 billion USD, or about 56% of current expenditures, as reported in my presentation, Freedom for Scholarship in the Internet Age. This is a conservative estimate in many respects.
This letter understates the current extent of open access. Bjork et al., based on 2006 data, reported that 4.6% of the world's scholarly peer-reviewed journal articles were published open access, with more made freely available by publishers after a delay period, resulting in over 8% of articles made freely available by publishers within a year of publication. Factoring in green self-archiving, the total of freely available fulltext after 2 years was close to 20%. Since 2006, open access has continued to grow dramatically, as I report regularly in my series, The Dramatic Growth of Open Access.
Please note that my focus on this one bullet point does not imply my agreement with the remainder of the letter; rather I thought it important to highlight this particular issue.