The evolution of unit labor costs will also reflect the growth of output per hour. Over the past decade, the U.S. economy has benefited from a remarkable acceleration of productivity: Strong gains in efficiency have buoyed real incomes and restrained inflation. But experience suggests that such rapid advances are unlikely to be maintained in an economy that has reached the cutting edge of technology. Over the past two years, growth in output per hour seems to have moved off the peak that it reached in 2003. However, the cause, extent, and duration of that slowdown are not yet clear. The traditional measure of the growth in output per hour, which is based on output as measured from the product side of the national accounts, has slowed sharply in recent quarters. But a conceptually equivalent measure that uses output measured from the income side has slowed far less. Given the divergence between these two readings, a reasonably accurate determination of the extent of the recent slowing in productivity growth and its parsing into cyclical and secular influences will require the accumulation of more evidence.

Two distinct but overlapping developments appear to be at work: a longer-term trend decline in bond yields and an acceleration of that trend of late. Both developments are particularly evident in the interest rate applying to the one-year period ending ten years from today that can be inferred from the U.S. Treasury yield curve. In 1994, that so-called forward rate exceeded 8 percent. By mid-2004, it had declined to about 6-1/2 percent--an easing of about 15 basis points per year on average. Over the past year, that drop steepened, and the forward rate fell 130 basis points to less than 5 percent.

Some, but not all, of the decade-long trend decline in that forward yield can be ascribed to expectations of lower inflation, a reduced risk premium resulting from less inflation volatility, and a smaller real term premium that seems due to a moderation of the business cycle over the past few decades. This decline in inflation expectations and risk premiums is a signal development. As I noted in my testimony before this Committee in February, the effective productive capacity of the global economy has substantially increased, in part because of the breakup of the Soviet Union and the integration of China and India into the global marketplace. And this increase in capacity, in turn, has doubtless contributed to expectations of lower inflation and lower inflation-risk premiums.

In addition to these factors, the trend reduction worldwide in long-term yields surely reflects an excess of intended saving over intended investment. This configuration is equivalent to an excess of the supply of funds relative to the demand for investment. What is unclear is whether the excess is due to a glut of saving or a shortfall of investment. Because intended capital investment is to some extent driven by forces independent of those governing intended saving, the gap between intended saving and investment can be quite wide and variable. It is real interest rates that bring actual capital investment worldwide and its means of financing, global saving, into equality. We can directly observe only the actual flows, not the saving and investment tendencies. Nonetheless, as best we can judge, both high levels of intended saving and low levels of intended investment have combined to lower real long-term interest rates over the past decade.

Since the mid-1990s, a significant increase in the share of world gross domestic product (GDP) produced by economies with persistently above-average saving--prominently the emerging economies of Asia--has put upward pressure on world saving. These pressures have been supplemented by shifts in income toward the oil-exporting countries, which more recently have built surpluses because of steep increases in oil prices. The changes in shares of world GDP, however, have had little effect on actual world capital investment as a percentage of GDP. The fact that investment as a percentage of GDP apparently changed little when real interest rates were falling, even adjusting for the shift in the shares of world GDP, suggests that, on average, countries' investment propensities had been declining.