The Dollar as an Irrational Speculative Bubble

Several recent developments have inspired us to consider a non-standard model of the dollar as a speculative bubble without the constraint of fully rational expectations: (1) the dollar continued to rise in 1984 after real interest rate differentials and other fundamentals began moving the wrong way; (2) the results of market efficiency tests imply, that the rationally expected rate of dollar depreciation has been less than the forward discount; (3) Krugman-Marris current account calculations suggest that the rationally expected rate of depreciation is greater than the forward discount; (4) survey data show an expected rate of depreciation that is also greater than the forward discount; (5) the hypothesis of a "safe-haven" shift into U.S. assets and a decrease in the U.S. risk premium, which would explain some of the foregoing, is contradicted by a decline in the differential between off shore interest rates (covered) and U.S. interest rates. Our model features three classes of actors: fundamentalists, chartists and portfolio managers. Fundamentalists forecast a depreciation of the dollar based on an overshooting model that would be rational if there were no chartists. Chartists ex