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Chapter 6 Chapter 6

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19<br />

Limitations of Modified Duration:<br />

Modified duration is a measure of rate of change in the bond price on change in<br />

yield to maturity. Suppose the modified duration is 2. It means for every 1<br />

percentage point change in YTM, the bond value will change inversely by 2%.<br />

Suppose the current value of a bond is Rs.90 and YTM is 10%; if YTM increases<br />

to 11% , the value of bond will be Rs.88.20; if the YTM decreases to 8%, the<br />

value of the bond will be Rs.91.80.<br />

Let us understand this point more clearly. Suppose (i) the current value of a bond<br />

is Rs.90 (ii) YTM is 10% and (iii) Modified duration is 1. The following table gives<br />

change in Bond price on various changes in YTMs.<br />

Change in YTM ( in terms % change in bond price Bond value<br />

of basis points)<br />

-100 + 1% 90.90<br />

+ 100 - 1% 89.10<br />

- 200 +2% 91.80<br />

+200 -2% 88.20<br />

-300 +3% 92.70<br />

+300 -3% 87.30<br />

-400 +4% 93.60<br />

+400 -4% 86.40<br />

The above data concludes that the relationship between YTM and bond value is<br />

linear and inverse i.e. if we draw graph using the above data (taking YTM on y-<br />

axis and bond value on x-axis), we will obtain a downward moving straight line<br />

i.e. the graph of the relationship between price and YTM is in the form of a down<br />

ward moving straight line.<br />

The realty (with respect to linearity), however, is different i.e. the true<br />

relationship between a change in price of bond and a change in YTM is not linear.<br />

Duration provides an approximation of this relationship. For a small change in<br />

YTM, duration estimates the changed price more or less accurately, but for<br />

larger changes duration becomes less accurate.<br />

Q. No. 29 : 10 % bond with maturity 5 years. Face value Rs.100. Current YTM is<br />

10%.<br />

(a)<br />

(i) Find value of the bond.<br />

(ii) What will be the value of the bond if the YTM increases from 10% to 11%<br />

(iii) What will be the value of the bond if the YTM decreases from 10% to 9%<br />

(iv) What will be the value of the bond if the YTM increases from 10% to 12%<br />

(v) What will be the value of the bond if the YTM decreases from 10% to 8%<br />

(b) Find modified duration. Using modified duration:

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