Treasury ceased publication of the 30-year constant maturity series on
February 18, 2002 and resumed that series on February 9, 2006.
To estimate a 30-year rate during that time frame, this series includes the
Treasury 20-year Constant Maturity rate and an "adjustment factor," which may be
added to the 20-year rate to estimate a 30-year rate during the period of time in
which Treasury did not issue the 30-year bonds.