* O'Sullivan, Arthur; Steven M. Sheffrin (2003). Economics: Principles in Action. Pearson: Prentice Hall. pp. 243. ISBN 0-13-063085-3 | * O'Sullivan, Arthur; Steven M. Sheffrin (2003). Economics: Principles in Action. Pearson: Prentice Hall. pp. 243. ISBN 0-13-063085-3 |