Bond Pricing and Immunization Strategy - Asset Allocation in Bond Investment
Bond Pricing and Immunization Strategy - Asset Allocation in Bond Investment
ABSTRACT
Asset allocation is a widely used financial term that fits most people. However, even in the most basic concept of asset
allocation, there is still existing risk or uncertainty. This paper aims to discuss the impact of different influencing
factors on bond pricing in the bond market and then further discuss the risk aversion strategy that can be analyzed
through the duration, also known as the immunization strategy. We also conduct sensitivity analysis of four different
situations, changing different yield rates and coupons and changing increasing yield rates and coupons at a certain
rate. This paper found that different yield rates, different coupons, and increasing yield rates have a linear relationship
with the bond price. In contrast, the increasing coupon with a certain ratio has a nonlinear relationship. Through
immunization strategy, it can develop an asset portfolio composed by a certain ratio. Also, using the immunization
strategy can reduce the risks that investors need to take and maximize their interests to a certain extent. The
combination of a certain percentage of zero-coupon government bonds and corporate bonds effectively shields
investors from risk. This paper constructs the issue of bond pricing, which is of practical significance for investors to
evaluate their risk-bearing ability and purchasing ability and to use the immunization strategy of hedging risk.
1.      INTRODUCTION
                                                                 is of greatest concern. Therefore, many investors turn to
    Bonds are one kind of debt security issued in                various bond management strategies to protect their
connection with a borrowing arrangement that obligates           bond portfolio from interest rate risk. There are overall
the issuer to make specified payments to the                     two categories of bond management strategies: passive
bondholders on specified dates [1]. Among all debt               strategy and active strategy. This article will mainly
securities, including those in the money market and the          focus on immunization strategy, one passive bond
capital market, bonds are among the most common                  management strategy used by many financial and funds
long-term debt securities traded in the capital market. A        institutions.
developed bond market can provide local firms with
                                                                     Next, we will review the literature on bond pricing
access to direct financing, enhance the liquidity of the
                                                                 and immunization strategy. For defaultable bonds,
overall market and reduce systematic risk in the market
                                                                 general pricing methods can be divided into two main
[2]. Therefore, given the importance of the bond market,
                                                                 categories: structural models originated from the pricing
how to price bonds traded in the bond market precisely
                                                                 model proposed by Merton and reduced-form models or
is one top priority for the healthy and sustainable
                                                                 intensity models. Merton presented a simplified model
development of the bond market.
                                                                 that can value each component of the firm’s liability
    Moreover, bonds traded in the capital market are             mix. Despite being simple and innovative, Merton’s
exposed to various kinds of risks, including default risk,       pricing model was inevitably subject to its simplified
liquidity risk, and interest rate risk, and so on. For most      assumptions about its liability structure and costless
bond portfolio managers, the sensitivity of bond prices          bankruptcy. Therefore, many scholars, including Black
to changes in market interest rates, that is, interest rate      and Cox, Leland and Fan, and Sundaresan, had
risk                                                             incorporated more realistic assumptions into the Merton
                                                                 model [3]. For the default-free bond, Longstaff and
Schwartz found that the risk of a default-free bond            immunization strategy and mentions immunization
stems from two major sources: interest rate shifts and         strategy’s limitations; Section 6 presents our conclusions.
changes in bond market volatility, and that changes in
the volatility of interest rates have the greatest impact
                                                               2.   BACKGROUND DESCRIPTION
on the prices and yields of intermediate-term bonds [4].
    Over the past few decades, there are lots of studies           Macaulay duration is of great significance to bond
focusing on bond portfolio management. Redington, in           pricing. The calculated Macaulay duration can be
1952 first introduced the concept of immunization based        combined with an immunization strategy to help
on the assumption of flat term-structure [5]. Later,           investors avoid risks [7].
Fisher and Weil in 1971 modified Redington’s approach              According to Frederick Robertson Macaulay’s
and expanded immunization strategy by taking into              research, bond interest rate, maturity period, and yield to
account the natural shifts of interest rate [6]. After 1971,   maturity are closely related to bond price. He proposed
several more advanced theories about immunization              five theorems of bond pricing that are still regarded as
strategies were continuously proposed, including               classic nowadays.
Bierwag and Khang’s maximin theory, Leibowitz and
Weinberger’s contingent immunization, and Bierwag                  In this research, we conduct about the relationship
and Khang’s multiple shocks, and so on.                        between bond price and different factors. Generally
                                                               speaking, bond pricing is divided into two dimensions:
    In the paper, we first introduced discounted cash          internal and external factors. Internal factors include the
flow concepts, duration, and modified duration.                face value, the coupon interest; the validity period;
Secondly, we listed the pricing methods, including zero-       whether it can be redeemed in advance; whether it is
coupon bonds, fixed-rate coupon bonds, and floating-           convertible; liquidity, and the possibility of default.
rate coupon bonds. And then conducted a sensitivity            External factors include risk-free interest rates, market
analysis of bond prices when changing bond yield rates         interest rates, and inflation rates [8].
and coupon rates, respectively. After that, we studied
one passive bond management strategy, immunization                 Bond price always depends on his present value. The
strategy, and conducted an empirical test to construct         present value in accounting measurement refers to the
one real situation where one investor needs to construct       future cash flow value after being discounted at an
his bond portfolio to fund future payment and test the         appropriate rate. It is a measurement attribute that
effectiveness of immunization strategy. In the last, we        considers the time value of money. To understand how
listed some limitations about immunization strategy.           to price a particular bond, the concept of present value
                                                               should be introduced first, which is needed to be
    As for the sensitivity analysis found that bond prices     obtained in the calculation and has some practical
and bond yields generally show an inverse relationship.        significance for the understanding duration. Generally
When other conditions remain unchanged, as the yield           speaking, there are two big categories of bonds: fixed-
rate increases at the same amount, the bond price falls at     rate bonds and floating-rate bonds. A zero-coupon bond
a certain rate; while the yield rate increases at a certain    is a kind of fixed-rate bond where the coupon rate
rate, the price of the bond falls more and more sharply. It    equals zero. This kind of bond is issued at a discount,
is generally a positive correlation between bond price         does not carry coupons, and pays a lump sum of
and coupon. When other conditions remain unchanged,            principal and interest at face value on maturity.
as the coupon (coupon rate) increases at the same
amount, the price of the bond increases at a certain rate,         The immunization strategy is aimed to manage the
while the coupon (coupon rate) increases at a certain          bond portfolio. For any bond, interest rate fluctuations
rate, the price of the bond goes up more and more              have opposite effects on long-term and short-term bonds
dramatically. As for the empirical test, we found that one     [9]. By selecting a bond portfolio with a Macaulay
constructed bond portfolio can be immunized from the           duration equal to the maturity of its liabilities (cash
fluctuation of interest rate when the interest rate changes    outflow), the manager can ensure a fixed cash flow after
insignificantly. But as time goes by, the duration of          a certain period by taking advantage of the offset
bonds and the duration of liability do not match, which        characteristics of price risk and reinvestment risk.
means that the investors need to rebalance their bond              This paper aims to propose an immunization strategy
portfolio.                                                     by integrating different bond varieties, which can lower
    The remainder of the paper is organized as follows:        the risk for the investors.
Section 2 describes basic background about bond
pricing, Macaulay duration, and immunization strategy;         3.   PRICING THE BOND
Section 3 introduces bond pricing methods for different
kinds of bonds and performs one sensitivity analysis of            Bond pricing is for risk management, so as
bond prices; Section 4 describes modified duration             important as price is the sensitivity of the bond. For
based on the Macaulay duration; Section 5 introduces           interest rate sensitivity, the most important is duration
immunization strategy, conducts an empirical test for          and convexity.
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                            Advances in Economics, Business and Management Research, volume
Mathematically, you can use these two to approximate a              P0 is the price of the zero-coupon bond, F is the face
bond as a quadratic function. More importantly, the
                                                                value of a bond, r is yield to maturity (YTM), and n is
values and symbols of the two reflect important
                                                                the number of periods to maturity.
characteristics of bonds. For example, the convexity of a
normal bond is positive, but it's negative for mortgage-            When we plug the zero-coupon pricing formula into
backed security (MBS). The reason is that when the              the general duration formula above, we get the
interest rate is low, the price of ordinary bonds will rise,    following formula:
but the price of MBS tends to level off. When the
                                                                                             𝐷0 = 𝑛                  (4)
interest rate is low, the buyers will choose to exercise
the second loan to pay off the original high-interest              D0 is the duration of a zero-coupon bond, n is the
mortgage, making it difficult for the price to exceed the       number of periods to maturity.
parity.
    This paper mainly discusses bond pricing based on           3.2. Fixed-Rate Bond
mathematical methods, which uses interest rate and
coupon to calculate the present value of bonds. In                  Fixed-rate bonds are bonds that pay the same
addition, this paper will compare the influence of              interest rate for the entire term of the bond. Investors
different factors on the present value of bonds and             can choose from fixed-rate bonds in the form of treasury
combine the concept of duration to make a tentative             bills, corporate bonds, municipal bonds, or certificates
plan of immunization strategy.                                  of deposit if they want a guaranteed interest rate for a
                                                                specified period.
   The following is the mathematical formula for the
present value of bonds:
              𝑃 = ∑𝑛
                           𝐶            𝐹                 (1)   3.3. Floating Rate Bond
                           𝑛
                      𝑖=1 (1+𝑟)𝑛
                                    +
                                        (1+𝑟)𝑛
                                                                    A floating rate fund is a fund that invests in financial
   where C is periodic coupon payment, F is the face            instruments that pays a variable or floating interest rate
value of a bond, r is yield to maturity (YTM), n is the         [11]. A floating rate fund, which can be a mutual fund
number of periods to maturity.                                  or an exchange-traded fund (ETF), invests in bonds and
  The following formula is used to calculate the                debt instruments whose interest payments fluctuate with
Macaulay duration [10]:                                         an underlying interest rate level. Typically, a fixed-rate
                                     𝐶𝐹𝑛                        investment will have a stable, predictable income.
                          𝑛
                                    (1+𝑟)𝑛
                                                                However, as interest rates rise, fixed-rate investments
                    𝐷
                          𝑖=1
                                𝑛                         (2)
                                        𝑃                       lag behind the market since their returns remain fixed.
                                                                Floating rate funds aim to provide investors with a
   where, CF is periodic cash flow, P is the present            flexible interest income in a rising rate environment. As
value of a bond, r is yield to maturity (YTM), n is the         a result, floating-rate funds have gained popularity as
number of periods to maturity.                                  investors look to boost the yield of their portfolios.
                         𝑃0
                                = (1+𝑟)𝑛
                                        𝐹                 (3)
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where, ∆𝑃 refers to the monetary change of bond’s                of Life-Office Valuations’ in 1952. He assumed a flat
price; P refers to bond’s price; y refers to the bond’s          term structure and then showed that if the duration of an
yield to maturity.                                               asset portfolio matched the duration of liabilities,
                                                                 changes in interest rates over time would affect the
    From the perspective of calculus, the modified
                                                                 value of liabilities to the same extent as these changes
duration can be expressed as the first derivative of the
                                                                 affected the value of assets.[14]
bond’s price with respect to changes in the bond’s
yield divided by bond price. Thus, the formula for the               There are overall two steps in using the
modified duration can also be expressed as:                      immunization strategy. The first step is to match the
                                                                 duration of asset and liability investors hold in their
                                                                 portfolios. The same
                                  1       𝑑
                      𝐷∗ = −              𝑃              (8)     asset and liability duration implies that assets and
                         ×                𝑑𝑦                     liabilities have the same sensitivity to interest rate
                                 𝑃
    In this way, the percentage of a bond’s price change         fluctuation.
is just the product of modified duration and the change
                                                                      The formula can be expressed as below:
in bond’s yield, which makes the calculation much
easier
                                                                                    𝑛                  𝑚
than before.                                                                       ∑𝑖=1 𝐷𝑖 ×       =   𝑗=𝑖   𝐷𝑗 ×       (9)
                                                                                        𝑤𝑖                   𝑤𝑗
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                             Advances in Economics, Business and Management Research, volume
    Di refers to the duration of bond i; wi refers to the       unit of each bond, we can get the exact units needed to be
portfolio share of bond i; Dj refers to the duration of         bought.
liability j; wj refers to the share of liability j.
                                                                    Through the calculations, the units of government
    The second step is to match the present value of            bond and corporate bond needed to be bought
assets and liabilities. These two rules can, to some            respectively are 90.07 and 74.14.
extent, guarantee that assets’ and liabilities’ value
change can offset against each other when interest rate             Therefore, from the above working process, we can
fluctuates.                                                     conclude that the student should allocate 50.94% of his
                                                                fund to invest zero-coupon bond and 49.06% of his fund
                                                                to invest corporate coupon bond to make the one-off
5.2. Empirical test
                                                                payment three years later.
5.2.1. Constructing the empirical model
                                                                5.2.2. Testing the effect of change of interest rate
    In this section, we made an empirical test to examine
                                                                    After constructing the portfolio, the next thing we
the effectiveness of the immunization strategy.
                                                                need to do is to test its immunization effect, that is,
    Try to assume that one student will need to make a          whether this strategy can shield the portfolio from
one-off tuition payment of $17,000 after three years            interest risk.
from now. He wonders how to construct the portfolio to
                                                                    Therefore, we list several scenarios to simulate the
fund future payments. There are two kinds of bonds in
                                                                fluctuation of interest rates in the market.
the financial market:
                                                                    And in each scenario, we can calculate the value of
   The first is one zero-coupon government bond, with
                                                                assets after three years. The formula of the future value
a face value of $100, a current price of $85.48, and
                                                                of assets is given below:
remaining life of 4 years.
                                                                      Future value of assets
    The second is one corporate bond, with a face value
of $100, the current price of $100, an annual coupon of               = value of zero-coupon bond + value of coupon bond
$4, and remaining life of 2 years.
    Assume all debt has the same level of default risk.
The benchmark yield curve for fixed-income                              =
                                                                            face value of zero−coupon bond   × units +
                                                                                  (1+discount rate)
investments of the same riskiness is flat at a level of 4%            annual coupon of corporate bond
p.a.                                                              [        (1+discount rate)2           +
                                                                annual coupon+face value
    Using the Macaulay duration formula, we can                                             ] × units
                                                                      (1+discount rate)                                  (
calculate the duration of the zero-coupon bond and the
corporate bond, respectively 4 years and 1.96 years.               Figure 5 gives the sensitivity of the future value of
   What is more, the duration of the liability is three         assets on changes in the interest rate, in a wide range
years.                                                          between 2.5% and 5.5%.
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5.3 Some limitations about immunization                         This paper discusses three aspects: bond pricing
strategy                                                      modified duration and immunization strategy.
    According to the above analysis, there still exist            Firstly, we use sensitivity analysis to study the effect
some limitations to the immunization strategy. First, the     of yield rate and coupon rate on the bond price under
duration of bonds will be affected by various factors,        different growth conditions. Secondly, we give some
including bonds’ residual maturity and interest rate,         details on the modified duration to simplify the
which can be directly seen through the formula of             calculation of bonds’ price change when a percentage
Macaulay duration. The change of interest rate will           change of bond’s yield is given. To be more specific, the
influence the expected stream of each future payment          percentage of a bond’s price change is just the product
and thus the price of a bond. Thus, when the interest         of modified duration and the change in the bond’s yield.
rate changes, the duration of one bond will inevitably        Thirdly, from the empirical test, it can be known that
vary. Even if we assume that the interest rate does not       once the investor matches the duration of the bond
change, the bonds’ duration will still change with time.      portfolio and the duration of liability, the investor can
For coupon bonds, duration generally decreases less           shield his portfolio from the fluctuation of interest rate
rapidly than maturities dose. However, for the one-off        when it changes insignificantly. However, there are
payment liability, its duration equals its maturity. Thus,    some limitations to the immunization strategy, including
as time passes, bond portfolio and liability duration will    rebalancing, duration limitations, and the assumption of
fall at different rates [15].                                 the flat term structure of interest. There is a possible
                                                              portfolio of bonds by using the immunization strategy.
    Therefore, when these factors change, the duration        The first is one zero-coupon government bond, with a
of bonds varies as well. The duration of assets and that      face value of $100, a current price of $85.48, and
of liability become unmatched. The immunization               remaining life of 4 years. The second is one corporate
strategy necessitates continuous rebalancing so that          bond, with a face value of $100, a current price of $100,
investors can guarantee that their portfolio is well          an annual coupon of $4, and remaining life of 2 years.
immunized.                                                    Therefore, from the above working process, we can
    Secondly, because immunization strategy is based          conclude that the student should allocate 50.94% of his
on duration, immunization strategy is inevitably subject      fund to invest zero-coupon bond and 49.06% of his fund
to the limitation of duration. According to the modified      to invest corporate coupon bond to make the one-off
duration formula, which directly derives from Macaulay        payment three years later.
duration, we know that it implies that the percentage of          Although this paper has a sufficient theoretical
a bond’s price change is directly proportional to the         structure and derivation process, it still has some defects
change in the bond’s yield. However, if we draw the           in the actual process of data collection and innovative
graph of the percentage change in bond price as a             modeling. In addition, according to the actual policy and
function of the change in its yield, it can be obviously      the current situation of the world economic
found that the plot is not linear. For small changes in       environment, this paper should also make some
bond yield, the duration’s approximation is quite             corresponding mention and adjustment. Future research
accurate, while for significant changes in bond yield, the    should pay more attention to the macro direction of the
duration’s approximation is inaccurate to some extent.        world economy to provide the detailed allocation of
    Thirdly, the immunization strategy mentioned before       bond portfolio and data simulation results for
is based on the concept proposed by F.M.Redington. He         subsequent researchers to study
assumed the term structure of interest to be flat so that
the constant discount rate would be applied to discount       REFERENCES
all the cash flows generated by holding bonds.[16]
However, this assumption is unrealistic because of the        [1]. Zvi Bodie, & Alex Kane. (2011). Investments (9th
frequent shifts in the term structure of interest rates            edition)
during the holding period. Therefore, Redington’s             [2]. Ivanova, Y. P. (2004). Developing domestic bond
measure of duration does not provide an accurate                   markets: Importance, alternatives, prerequisites and
measure for changes in the pattern of the discount rate.           sequence (Order No. 1463331).
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