PickStock (copyright 2003, Bell Software and Services, Inc.) uses principal components analysis to search out potentially underpriced stocks by analyzing a user-supplied database of historical stock prices. The program is believed to be an implementation of what is known as 'arbitrage pricing theory' (see for example S. Ross, 'The arbitrage theory of capital asset pricing', J. Economic Theory, vol. 13, pp. 341-360, 1976).