BKM Chapter 16 Flashcards
Properties of bond prices (6, aka bond-pricing relationships)
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bond prices are:
- inversely related to yields
- more sensitive to decreases in yields than increases
- long-term bond prices are more sensitive to yield changes than short-term bond prices
- sensitivity of bond prices to yield changes increases at a decreasing rate as maturity increases
- prices of low-coupon bonds are more sensitive to change in yield than prices of high-coupon bonds
- sensitivity of bond price to change in yield is inversely related to the yield at which it is currently selling
Reason bond prices for long-term bonds are more sensitive to yield changes
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more distant CFs will be more heavily discounted, resulting in a larger price reduction
Effective maturity (aka Macaulay’s duration or duration)
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measure of interest rate risk/sensitivity
effective maturity = weighted average maturity of all CFs where the weights are the discounted CFs / total bond price
Modified duration (D*)
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D* = D / (1 + y / k)
where y = YTM
Linear approximation of the change in bond price from a change in interest rates (% change in bond price) (2 formulas)
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% change in bond price = - D * (change in y / (1 + y / k))
or = - modified duration * change in y
**works best for small changes in yields
Duration rules (5)
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- for a zero-coupon bond, duration = maturity
- holding maturity constant, duration is lower when coupon rates are higher
- holding coupon rates constant, duration increases as maturity increases (always true for bonds selling at or above par value)
- holding other factors constant, duration increases as YTM decreases
- duration of a perpetuity (w/maturity = infinity) = (1 + y) / y
PV(perpetuity)
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PV(perpetuity) = perpetuity payment / y
Duration and coupon rate relationship for perpetuities
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duration and coupon rate are independent - ONLY true for perpetuities
Duration linear approximation to change in bond prices and actual change in bond prices
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duration approximation always understates bond price (b/c the actual price change is convex)
understates the increase in bond price when yield decreases &
overstates the decrease in bond price when yield increases
*curves are tangent at the initial yield
Convexity adjustment to the duration price change approximation
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% change in bond price = -modified duration * change in y + .5 * convexity * (change in y)^2
Convexity (formula for the convexity variable in the convexity adjustment to the duration approximation)
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Convexity = [sum over all times, t, of PV(CF(t)) * (t^2 + t / k)] / (Price * (1 + y / k)^2)
Reason that convexity is desirable
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because convex bonds increase more in price when yields decrease than they decrease in price when yields increase ( = attractive asymmetry)
“Price” for greater convexity
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bond prices are more expensive and they tend to have lower yields
Convexity of callable bonds and duration approximation
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has a region of negative convexity with low interest rates near the call price (max price at y intercept) and positive convexity at higher interest rates
in the region of negative convexity, the duration approximation overstates bond value
Effective duration for callable bonds
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cannot use the normal effective duration b/c future CFs are unknown (b/c the bond can be terminated)
effective duration = ((max price - min price) / current price) / (max rate - min rate)
Differences between the effective duration for callable bonds and the normal Macaulay duration (2)
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- uses the change in interest rate b/c maturity is variable
- relies on option pricing methodology that accounts for interest rate variability
Interpretation of the effective duration for callable bonds
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bond price changes by the effective duration % for a r percentage point change in market interest rates around current values
Mortgage-backed securities (aka pass-throughs)
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many mortgages pooled together and sold on the fixed-income market
homeowner > pays lender > pays federal agency > pays purchaser of MBS
early termination of mortgage loan from a homeowners option to refinance is similar to a call provision for a bond
Main difference b/w mortgage-backed securities and callable bonds
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“call price” = remaining balance of the mortgage loan, but because homeowners do not always refinance, it’s possible for the bond price > principal balance
> > means that the call price is not a firm ceiling on bond price