Sullivan, Arthur; Steven M. Sheffrin (2022). Economics. Paramus, New Jersey: Savvas Learning Company. p. 471. ISBN0-13-063085-3. Archived from the original on 2016-12-20. Retrieved 2009-07-30.
Sullivan, Arthur; Steven M. Sheffrin (2022). Economics. Paramus, New Jersey: Savvas Learning Company. p. 471. ISBN0-13-063085-3. Archived from the original on 2016-12-20. Retrieved 2009-07-30.