↑ O'Sullivan, Arthur; Sheffrin, Steven M. (2003). Economics: Principles in Action. Upper Saddle River, New Jersey: Pearson Prentice Hall. p. 272. ISBN978-0-13-063085-8.
↑ J. Downes, J. E. Goodman, Dictionary of Finance & Investment Terms, Barron's Financial Guides, 2003
1 2 J. Downes, J. E. Goodman, Dictionary of Finance & Investment Terms, Barron's Financial Guides, 2003; and J. G. Siegel, N. Dauber & J. K. Shim, The Vest Pocket CPA, Wiley, 2005.