More than half of all peer-reviewed research articles published from 2007 to 2012 are now free to download somewhere on the Internet, according to a report produced for the European Commission, published today. That is a step up from the situation last year, when only one year – 2011 – reached the 50% free mark. But the report also underlines how availability dips in the most recent year, because many papers are only made free after a delay.

“A substantial part of the material openly available is relatively old, or as some would say, outdated,” writes Science-Metrix, a consultancy in Montreal, Canada, who conducted the study, one of a series of reports on open access policies and open data.

The study (which has not been formally peer-reviewed) forms part of the European Commission’s efforts to track the evolution of open access. Science-Metrix uses automated software to search online for hundreds of thousands of papers from the Scopus database.

The company finds that the proportion of new papers published directly in open-access journals reached almost 13% in 2012. The bulk of the Internet’s free papers are available through other means – made open by publishers after a delay, or by authors archiving their manuscripts online. But their proportion of the total seems to have stuck at around 40% for the past few years. That apparent lack of impetus is partly because of a ‘backfilling’ effect, whereby the past is made to look more open as authors upload versions of older paywalled papers into online repositories, the report says. During this last year, for instance, close to 14,000 papers originally published in 1996 were made available for free.

“The fundamental problem highlighted by the Science-Metrix findings is timing,” writes Stevan Harnad, an open-access advocate and cognitive scientist at the University of Quebec in Montreal, Canada. “Over 50% of all articles published between 2007 and 2012 are freely available today. But the trouble is that their percentage in the most critical years, namely, the 1-2 years following publication, is far lower than that. This is partly because of publisher open access embargoes, partly because of author fears and sluggishness, but mostly because not enough strong, effective open access mandates have as yet been adopted by institutions and funders.”

The report’s conclusions are only estimates, as the automated software does not pick up every free paper, and this incompleteness must be adjusted for in the figures (typically adding around 5-6% to the total, a margin calculated by testing the software on a smaller, hand-checked sample of papers). And many of the articles, although free to read, do not meet formal definitions of open access – for example, they do not include details on whether readers can freely reuse the material. Éric Archambault, the founder and president of Science-Metrix, says it is still hard to track different kinds of open manuscripts, and when they became free to read.

The proportion of free papers also differs by country and by subject. Biomedical research (71% estimated free between 2011 and 2013) is far more open than chemistry (39%), for example. The study suggests that from 2008-2013, the world’s average was 54%, with Brazil (76%) and the Netherlands (74%) particularly high. The United Kingdom, where the nation’s main public funder, Research Councils UK, has set a 45% target for 2013-14, has already reached 64% in previous years, the report suggests.

The study comes during Open Access week, which is seeing events around the world promoting the ideas of open access to research. Yesterday saw the launch of the ‘Open Access Button’ in London – a website and app that allows users to find free research. If no free copy is available, the app promises to email authors asking them to upload a free version of their paper – with an explanation direct from the user who needs the manuscript. “We are trying to make open access personal – setting up a conversation between the author and the person who wants access,” says Joe McArthur, who co-founded the project and works at the Right to Research Coalition, an advocacy group in London.