Measuring the Impact of Gold and Green Open Access

It was found that, for articles published between 2008 and 2015, 9% were available through gold open access routes and 13% were available through green routes; most were not openly accessible. Citation rates were comparable for green open access and non-open access articles, but citation rates for gold open access articles were lower. After controlling for publication year, citation rates of gold, green, and non-open access articles were comparable. Among gold open access articles, citation rates were highest for open access journals with article processing charges, but after controlling for publication year, articles published in hybrid journals, followed by those in open access journals with article processing charges, achieved the highest citation rates. Articles published in free open access journals had the lowest citation rates. The results suggest that green open access is the most economical approach to comply with open access policies, and that it provides researchers with at least as much research impact as gold open access.