Most open-access publishers charge fees that are much lower than the industry's average revenue, although there is a wide scatter between journals. The largest open-access publishers - BioMed Central and PLoS - charge $1,350-2,250 to publish peer-reviewed articles in many of their journals, although their most selective offerings charge $2,700-2,900. In a survey published last year2, economists Bo-Christer Björk of the Hanken School of Economics in Helsinki and David Solomon of Michigan State University in East Lansing looked at 100,697 articles published in 1,370 fee-charging open-access journals active in 2010 (about 40% of the fully open-access articles in that year), and found that charges ranged from $8 to $3,900. Higher charges tend to be found in 'hybrid' journals, in which publishers offer to make individual articles free in a publication that is otherwise paywalled (see 'Price of prestige').