The standard constant-maturity data put out by the Treasury Department are only an estimate of yields, because it is rare to find bonds maturing in exactly seven years, for example. In addition, these yields are for coupon bonds, including twice-yearly coupons. The yields on zero-coupon bonds provide a somewhat cleaner measure, despite the complications of tax differences and lower market liquidity. The two curves are similar, although the zero-coupon curve is somewhat steeper and generally lower. Yield spreads, particularly inversions, are often used to forecast recessions.
Low spreads indicate low real growth and high spreads indicate high real growth.