David J. Solomon and Bo‐Christer Björk published their research results on APC, or Article Processing Charges, in a paper titled Publication Fees in Open Access Publishing: Sources of Funding and Factors Influencing Choice of Journal.
In a survey they sent to 1,038 authors, a sample of which is available here, 429 authors (41%) responded, who recently published articles in 74 OA journals that charge APCs, stratified into seven discipline categories. The results to different questions studied are explained below.
1. What are the sources of the funding researcher/scholars are using to fund APC in different disciplines?
Solomon,Björk: Table 4
The source seems to vary significantly across the disciplines. While national and institutional funds seem to cover all disciplines, grants and contracts seem to be mostly reserved for the studies in Health Sciences and Biology and there are no examples of institutionally funded research in Arts and Architecture, Language and Literature, according to Table 4. Personal funds are still great source for APCs especially for Agriculture and Forestry and Business and Economics. As for the fee waiver, it seems like it is the most welcome occurrence for the humanities research, probably due to the mentioned lack of funds from institutions.
2. In answer to what are the factors influencing authors’ choice of the journal in which they published, Solomon and Björk claim: “Fit, quality, and speed of publication were the most important factors in the authors’ choice of a journal.”
Solomon,Björk: Graph - Factors Influencing the Joice of OA Journal
The graph proves that the OA status of the journal is slightly less important, although 60 % of the respondents judged this very important or important.
3. What is the maximum APC the authors are willing to pay to publish an article in a desired journal?
The responses ranged from $0 to $5,000 USD with an average amount of $649 and a standard deviation of $749. Also, in Table 6, the source of funding depending on the size of the APC is displayed:
Solomon, Björk: Table 6
4. Solomon and Björk also wanted to describe the authors in terms of publication experience, discipline, and country to better understand how these factors influence the funding of APCs and the authors’ choice of journals in which to publish their research. Table 5 shows the source of funding by authors’ country GNP category:
Solomon, Björk: Table 5
An interesting read from the Table 5 is that authors from countries with the GNP lower than 25,000 USD who receive less grants and funds, are more likely to pay from personal funds while authors from countries with the GNP over 25,000 USD are more likely to get their fee waived.
Find the entire pre-print version of the study here.
InTechOpen Blog 
NEVER PAY FOR GOLD OA BEFORE MANDATING GREEN OA
Harnad, S. (2011) Gold Open Access Publishing Must Not Be Allowed to Retard the Progress of Green Open Access Self-Archiving. Logos, 21 (3-4). pp. 86-93. http://eprints.ecs.soton.ac.uk/21818/
ABSTRACT: Universal Open Access (OA) is fully within the reach of the global research community: Research institutions and funders need merely mandate (green) OA self-archiving of the final, refereed drafts of all journal articles immediately upon acceptance for publication. The money to pay for gold OA publishing will only become available if universal green OA eventually makes subscriptions unsustainable. Paying for gold OA pre-emptively today, without first having mandated green OA not only squanders scarce money, but it delays the attainment of universal OA.
Harnad, S. (2010) No-Fault Peer Review Charges: The Price of Selectivity Need Not Be Access Denied or Delayed. D-Lib Magazine, 16 (7/8) http://www.dlib.org/dlib/july10/harnad/07harnad.html
ABSTRACT: Plans by universities and research funders to pay the costs of Open Access Publishing (“Gold OA”) are premature. Funds are short; 80% of journals (including virtually all the top journals) are still subscription-based, tying up the potential funds to pay for Gold OA; the asking price for Gold OA is still high; and there is concern that paying to publish may inflate acceptance rates and lower quality standards. What is needed now is for universities and funders to mandate OA self-archiving (of authors’ final peer-reviewed drafts, immediately upon acceptance for publication) (“Green OA”). That will provide immediate OA; and if and when universal Green OA should go on to make subscriptions unsustainable (because users are satisfied with just the Green OA versions) that will in turn induce journals to cut costs (print edition, online edition, access-provision, archiving), downsize to just providing the service of peer review, and convert to the Gold OA cost-recovery model; meanwhile, the subscription cancellations will have released the funds to pay these residual service costs. The natural way to charge for the service of peer review then will be on a “no-fault basis,” with the author’s institution or funder paying for each round of refereeing, regardless of outcome (acceptance, revision/re-refereeing, or rejection). This will minimize cost while protecting against inflated acceptance rates and decline in quality standards.
Thank you for summarizing our article. I just wanted to point out one misstatement in the summary. We surveyed 1,038 authors however 429 or just over 41% of the authors responded.
Dave Solomon
Thank you, David, this is now corrected in the blog post.