Comparing Carrots and Lettuce

Comments on Stephen Curry's "The inexorable rise of open access scientific publishing": The main difference between the Gargouri, Lariviere, Gingras, Carr & Harnad estimates of average percent Gold in the ISI sample (2.5%) and Laakso & Bjork's estimates (10.3% for 2010) probably arise because L&B's sample included all ISI articles per year for 12 years (2000-2011), whereas ours was a sample of 1300 articles per year, per discipline, separately, for each of 14 disciplines, for 6 years (2005-2010: a total of about 100,000 articles). Our sample was much smaller than L&B's because L&B were just counting total Gold articles, using DOAJ, whereas we were sending out a robot to look for Green OA versions on the Web for each of the 100,000 articles in our sample. It may be this equal sampling across disciplines that leads to our lower estimates of Gold: L&B's higher estimate may reflect the fact that certain disciplines are both more Gold and publish more articles (in our sample, Biomed was 7.9% Gold). Note that both studies agree on the annual growth rate of Gold (about 1%)