
FIXED INCOME SECURITIES 9-33
v.05/13/94 v-1.1
p.01/14/00
DURATION
Factors That Affect Bond Prices
In a competitive market, a company's bonds must offer fair expected
rates of return to entice investors. The return to the investor will be in
the form of price gains during the life of the bond plus the coupon
payments made by the issuer of the bond.
Sensitivity to
interest rates
In Unit Four, we discussed the relationship between market interest
rates and bond prices. We said that as interest rates fall, bond prices
rise and vice versa. For example, a bond with an 8% coupon will sell
at par (face value) when other competitive yields are also 8%. If the
market rate rises to 9%, the bond price will fall until its expected
return matches the 9% market rate.
Effect of
maturity on
sensitivity to
interest rates
So, we know that bond prices are sensitive to changes in market
interest rates. In addition, the prices of long-term bonds are more
sensitive to changes in interest rates than the prices of short-term
bonds. Given this relationship between the sensitivity of bond prices
to changes in market interest rates and the life of a bond, it is
particularly important to have an appropriate definition of the life or
term of a bond.
Effective life
of the bond
Just as the quoted coupon rate doesn't convey the true yield of a bond,
the effective life of a bond is more complicated than just looking at
the maturity date. Bond price sensitivity is more appropriately related
to the weighted average life of a bond than to the maturity date.
If you were to receive $1,000 after 20 years and no coupon
payments during that time, the effective life of the bond would be 20
years. However, if, in addition to the $1,000, you receive $100 per
year for each of the 20 years, the weighted average term of the
payout is less than 20 years. The higher the coupon payments
relative to the par value, the shorter the average life of the payout.