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The Yield Curve, September 2009

Since last month, the yield curve has steepened slightly, with long rates edging up as short rates edged down. The difference between these rates, the slope of the yield curve, has achieved some notoriety as a simple forecaster of economic growth. The rule of thumb is that an inverted yield curve (short rates above long rates) indicates a recession in about a year, and yield curve inversions have preceded each of the last seven recessions (as defined by the NBER). In particular, the yield curve inverted in August 2006, a bit more than a year before the current recession started in December, 2007. There have been two notable false positives: an inversion in late 1966 and a very flat curve in late 1998.

More generally, a flat curve indicates weak growth, and conversely, a steep curve indicates strong growth. One measure of slope, the spread between ten-year Treasury bonds and three-month Treasury bills, bears out this relation, particularly when real GDP growth is lagged a year to line up growth with the spread that predicts it.

Yield Curve Spread and Real GDP Growth
Yield Curve Spread and Lagged Real GDP Growth

Since last month, the three-month rate dipped to 0.11 percent (for the week ending September 18), down from August's 0.17 percent and July's 0.19 percent.

The ten-year rate dropped to 3.46 percent, down a mere 2 basis points from August's 3.48 and still below July's 3.62 percent. The slope increased to 335 basis points, up from August's 331 basis points but still down from July's 343 basis points. Projecting forward using past values of the spread and GDP growth suggests that real GDP will grow at about a 2.3 percent rate over the next year, the same prediction as last month. This is a bit below, but not that far from other forecasts.

Yield Curve Predicted GDP Growth

While such an approach predicts when growth is above or below average, it does not do so well in predicting the actual number, especially in the case of recessions. Thus, it is sometimes preferable to focus on using the yield curve to predict a discrete event: whether or not the economy is in recession. Looking at that relationship, the expected chance of the economy being in a recession next August stands at 3.0 percent, up from August's 2.6 percent, which was up from July's very low 1.8 percent. GDP revisions account for some of the increase in the numbers since July. See this article for more on the revisions.

The probability of recession coming out of the yield curve is very low, but remember that the forecast is for where the economy will be in a year, not where it is now. However, consider that in the spring of 2007, the yield curve was predicting a 40 percent chance of a recession in 2008, something that looked out of step with other forecasts at the time.

Another way to get at the question of when the recovery will start is to compare the duration of past recessions with the duration of the preceding interest rate inversions. The chart below makes the comparison for the recent period. The 1980 episode is anomalous, but in general longer inversions tend to be followed by longer recessions. Following this pattern, the current recession is already longer than expected.

Durations of Yield Curve Inversions and Recessions

Recession Duration (months)
Recession Yield curve inversion
(before and during recession)
1970 11 11
1973-1975 16 15
1980 6 17
1981-1982 16 11
1990-1991 8 5
2001 8 7
2008-present 20
(through August 2009)

Note: Yield curve inversions are not necessarily continuous month-to-month periods.
Sources: Bureau of Economic Analysis; Federal Reserve Board; and authors' calculations.

Of course, it might not be advisable to take these number quite so literally, for two reasons. (Not even counting Paul Krugman's concerns.) First, this probability is itself subject to error, as is the case with all statistical estimates. Second, other researchers have postulated that the underlying determinants of the yield spread today are materially different from the determinants that generated yield spreads during prior decades. Differences could arise from changes in international capital flows and inflation expectations, for example. The bottom line is that yield curves contain important information for business cycle analysis, but, like other indicators, should be interpreted with caution.

For more detail on these and other issues related to using the yield curve to predict recessions, see the CommentaryDoes the Yield Curve Signal Recession?

Recession Probability from Yield Curve

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