Institutional asset and liability management
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Institutional asset and liability management
Interest rate risk – Part III: Limitations of the Duration
model & Convexity
Key Learning objectives
Understand the relative strengths and weaknesses of the duration model
Understand the economic meaning of convexity & its properties
Consider adjustments to the duration model to incorporate convexity
Understand the impact of term structures and default risk
Understand the relative strengths and weaknesses of the duration model
Understand the economic meaning of convexity & its properties
Consider adjustments to the duration model to incorporate convexity
Understand the impact of term structures and default risk
Duration model and immunization strategies are useful tools for regulators
◼ The model used by APRA and BIS to monitor bank interest rate risk-taking is
heavily based on this model
Critics, however, claim that it is difficult to apply in real-world situations
Limitations of the duration model
Duration matching can be costly and time-consuming
◼ The impact of the growing purchased funds markets, asset securitization, loan sales markets
on balance sheet restructuring (speed and cost)?
◼ Taking hedging positions in derivative products?
Immunization is a dynamic problem
◼ Duration changes as the bond approaches maturity
◼ There is a trade-off between being perfectly immunized and the transaction costs
◼ So, most managers rebalance at discrete intervals (e.g., quarterly)
Limitations of the duration model
Large interest rate changes and convexity
◼ Duration measures the price sensitivity of fixed income securities for small (
in the order of 1 basis point) changes in interest rates
◼ When interest rate shocks are much larger, duration becomes a less accurate
predictor of interest rate sensitivity
◼ When R changes, D changes. Hence, D is not a constant.
Limitations of the duration model
Large interest rate changes and convexity
◼ Duration model predicts symmetric effects for rate increases and decreases on bond prices
◼ For large interest rate increases, duration model over-predicts the fall in bond prices while
for large interest rate decreases it under-predicts the increase in bond prices
Key Learning objectives
Understand the relative strengths and weaknesses of the duration model
Understand the economic meaning of convexity & its properties
Consider adjustments to the duration model to incorporate convexity
Understand the impact of term structures and default risk
Characteristics of Convexity
Convexity is desirable
◼ The greater the convexity of a security or a portfolio of securities, the more
insurance or interest rate protection an FI manager has against interest rate
increases and the greater the potential gains after interest rate decreases.
Convexity and duration
◼ The larger the interest rate changes and the more convex a fixed-income security
or portfolio, the greater the error the FI manager faces in using just duration to
immunize exposure to interest rate shocks.
All fixed-income securities are convex
Economic meaning of convexity
Point (A)
FV = $1,000
N = 6 (annual)
CR = R = 8%
P = $1,000
D = 4.993
Point (C)
FV = $1,000
N = 6 (annual)
CR = 8%
R = 10%
P = $912.895
Point (E)
FV = $1,000
N = 6 (annual)
CR = 8%
R = 6%
P = $1,098.347
Point (B)
Point (D)
Properties of convexity
❑ As the bond’s maturity (N)
increases, so does the convexity
(CX)
❑ Coupon bonds of the same maturity
(N) have less convexity (CX) than do
zero-coupon bonds
Properties of convexity
❑ For coupon bonds and discount or zero-coupon bonds of the same duration, part 3 of the table
shows that the coupon bond has more convexity.
Properties of convexity
❑ Assets are more convex than liabilities
Key Learning objectives
Understand the relative strengths and weaknesses of the duration model
Understand the economic meaning of convexity & its properties
Consider adjustments to the duration model to incorporate convexity
Understand the impact of term structures and default risk
Basics of continuous compounding
Annual compounding
More frequent compounding
Daily Compounding
Continuous compounding
Basics of continuous compounding (CC)
When compounding frequency approaches infinity, m ≈ ∞
With CC, an amount A invested for n years at rate R grows to:
where e = 2.71828
So, when, A = 100, n = 1, and R = 0.1, future value of A is:
This is (to two decimal places) the same as the value with daily compounding:
Bond price and yield under CC
The relationship between the price P and its yield y is:
From this, it follows that…
The term in parenthesis above is the ratio of the present value of the Cashflow
(Ci) at time ti to the bond price
Convexity of a bond
The convexity of a bond is:
where, CX is the convexity measure, y is the bond’s yield measured with
continuous compounding, C is the cashflow and P is the market price of the bond
Please, note: The exact calculation of CX won’t be required in the assessments –
you will be given information related to CX if needed for calculating price
changes or returns.
=
σ=0
2−
A Graphic Illustration of Duration Approximation
Duration and Convexity
Duration (D) is the slope of the price–yield curve, and
◼ Essentially, the first-order effect (dP/dR) of an interest rate change on the bond’s
price is the price-yield curve slope effect—measured by Duration (D)
The second order effect (dP2/d2R) measures the change in the slope of the
price-yield curve
◼ This is the curvature, or convexity (CX), effect
There are other higher order effects ( from Taylor expansion series)
Can be ignored for practical purposes
Convexity of a bond and IR risk
Thus, incorporating convexity gives…
◼ The first term is the simple duration model
◼ The second term is the second-order effect/convexity/curvature adjustment
In modified duration term
The parameter CX reflects the degree of curvature in the price–yield curve at the
current yield level
◼ The degree to which the capital gain effect exceeds the capital loss effect for an equal
change in yields up or down.
Convexity of a bond and IR risk
Even the above equation is not complete, because CX also changes with interest rate
(just as D does).
Higher orders (up to infinity) of derivatives and interest rate changes should be added,
which should remind you of Taylor expansion in your advanced mathematics course.
However, we typically ignore higher orders of approximation errors because they are
typically trivial → how big could be (∆) be if n >= 3?
Key Learning objectives
Understand the relative strengths and weaknesses of the duration model
Understand the economic meaning of convexity & it’s properties
Consider adjustments to the duration model to incorporate convexity
Understand the impact of term structures and default risk