One of the services RePEc offers to authors is the discovery of citations, CitEc. This is a difficult undertaking as this needs to be done entirely automatically. As project leader José Manuel Barrueco Cruz discusses in a previous post, the reference section of a paper is extracted through a series of steps: pdf download, file conversion to PostScript, further conversion to plain text, identifying reference section. In each of these steps there are losses.
But even once the reference section is in hand, we are not out of trouble. One needs to identify where each reference starts and ends, then try to match it with something already in RePEc. Considering all the different citation styles, typos, and plain errors, this is a daunting task. Matches that are sufficiently close are counted as citations, matches that are in some grey zone are fed to the RePEc Author Service to solicit the author’s help in sorting them out. Below are a few examples of what is offered to authors, for the case of a classic article by Gary Becker, Kenneth Murphy and Robert Tamura, Human capital, fertility and economic growth:
-  Becker, G.; Murphy, K. ald Tamura, R. (1993)Humall capital, fertility ald ecollomic growth 01 Humall Capital, third editioll, Gary Becker.
- Becker, Gary S.; Murphy, Kevin M.; and Tamura, Robert. Human Capital, Fertility, and Econonric Growth, Journal of Political Economy, October 1990 98(5) Part 2, pp. S12-S37.
- Becker GS, Murphy KM, Tamura R (1990) Human capital, fertility and economic growth. J Polit Econ 98:S12–S37.
- 1-25. Kevin M. Murphy, and Robert Tamura, Human Capital, Fer- tility and Economic Growth, Journal of Political Economy, October
- BECKER, 0. S., K. M. MURPHY and R. TAMURA (1990) Human Capital, Fertility and Economic Growth, Journal of Political Economy 98, S 12-37.
-  Becker, G., Murphy, K. and Tamura, R. (1990), Human capital, fertility, and economic growth, Journal of Political Economy, vol. XCVIII, pp.12-37.
- Population and Development Review, Vol.12, Supplement: Below-Replacement Fertility in Industrial Societies: Causes, Consequences, Policies, pp. 69-76. Becker, Gary; Kevin Murphy, y Robert Tamura. (1990). Human Capital, Fertility and Economic Growth. The Journal of Political Economy, Vol.98, No.5, Part 2: The Problem of Development: A Conference of the Institute for the Study of Free Enterprise System, S12-S37.
- (March/April 1973 Supplement), S279-88. ______________ Kevin M. Murphy, and Robert Tamura, Human Capital, Fertility, and Economic Growth, Journal of Political Economy, XCVIII
- Becker, S. Gary, Kevin, M. Murphy and Tamura, Robert (1990). `Human Capital, Fertility, and Economic Growth The Journal of Political Economy, Vol. 98, Issue 5, Part 2, Oct. 1990, pp. S12-S37.
- Bankconference on developmenteconomics. ecker, Gary, KevinMurphy, and RobertTamura. 1990. Human Capital, Fertility, and EconomicGrowth., Journal of PoliticalEconomy 98, 5, Part 2, pp. S12-S37.
These examples show what can go wrong in the file conversion and how citing authors can make mistakes. Still, CitEc has been able to recognize there references, but is not sure enough about them.
This also highlights that we try to minimize errors, even if this means leaving good citations out. Other citations services may have a different approach.