Citation counts are correlated with other measures of scholarly/scientific performance and impact and can in some cases be enhanced by making a work open access by self-archiving the complete article on the web, publishing it in an open access journal, or publishing it as an Open access article in one of the Hybrid open access journals.
There also exists an H-index measure of an individual scientist's impact and citation record.
Bollen, J., Van de Sompel, H., Smith, J. and Luce, R. (2005) Toward alternative metrics of journal impact: A comparison of download and citation data Information Processing and Management, 41(6): 1419-1440
Brody, T. and Harnad, S. (2004) Comparing the Impact of Open Access (OA) vs. Non-OA Articles in the Same Journals D-Lib Magazine 10(6).
Brody, T., Harnad, S. and Carr, L. (2005) Earlier Web Usage Statistics as Predictors of Later Citation Impact Journal of the American Association for Information Science and Technology (JASIST).
Eysenbach G. (2006a) Citation Advantage of Open Access Articles. PLoS Biol. 2006;4(5) p. e157. Shows the Open Access citation advantage over non-Open Access papers, as well as a gold-OA over green-OA citation advantage. in the Proceedings of the National Academy of Sciences (PNAS) Eysenbach G (2006b) . The Open Access Advantage. J Med Internet Res 2006;8(2):e8 Some follow-up data to the Eysenbach PLoS Biol study
Garfield, E. (1955) Citation Indexes for Science: A New Dimension in Documentation through Association of Ideas. Science, Vol:122, No:3159, p. 108-111
Garfield, E. (1973) Citation Frequency as a Measure of Research Activity and Performance in Essays of an Information Scientist, 1: 406-408, 1962-73, Current Contents, 5
Garfield, E. (1998) The use of journal impact factors and citation analysis in the evaluation of science. 41st Annual Meeting of the Council of Biology Editors, Salt Lake City, UT, May 4 1998
Hajjem, C., Harnad, S. and Gingras, Y. (2005) Ten-Year Cross-Disciplinary Comparison of the Growth of Open Access and How It Increases Research Citation Impact IEEE Data Engineering Bulletin 28(4) pp. 39-47. The study analyzed 1,307,038 articles published across 12 years (1992-2003) in 10 disciplines (Biology, Psychology, Sociology, Health, Political Science, Economics, Education, Law, Business, Management). Comparing OA and NOA articles in the same journal/year, OA articles have consistently more citations (25%-250% varying with discipline and year)
Kurtz, M. J. , Eichhorn, G. , Accomazzi, A. , Grant, C. S. , Demleitner, M. , Murray, S. S. (2004) kurtz/IPM-abstract.html The Effect of Use and Access on Citations Information Processing and Management 41 (6): 1395-1402
Lawrence, S, (2001) Online or Invisible? Nature 411 (2001) (6837): 521. Landmark paper: First demonstration of the Open Access citation advantage for self-archived papers.
MacCallum CJ & Parthasarathy H (2006) Open access increases citation rate. PLoS Biol 4(5): e176. Editorial about the Eysenbach study
Moed, H. F. (2005a) Citation Analysis in Research Evaluation. NY Springer.
Moed, H. F. (2005b) Statistical Relationships Between Downloads and Citations at the Level of Individual Documents Within a Single Journal Journal of the American Society for Information Science and Technology, 56(10): 1088-1097.
Shadbolt, N., Brody, T., Carr, L. and Harnad, S. (2006) The Open Research Web: A Preview of the Optimal and the Inevitable In Jacobs, N., (Ed. Open Access: Key Strategic, Technical and Economic Aspects, chapter 21. Chandos