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A convertible security
or convertible is a
hybrid security with a provision for the convertible to be exchanged for some other
security. Usually, conversion is at the security holder's
option, but a
mandatory convertible security
requires conversion, usually according to some schedule.
Most convertibles are either
convertible
preferred stock or convertible bonds
issued by a corporation and
convertible to that corporation's
common stock any time, at the security holder's option. These standard
convertible securities are the topic of this article.
Convertible
securities have a par value, and their
yield is quoted as a
percentage of par. Each security may be converted into a fixed number of
common shares. That number is the security's
conversion ratio. For example, if a convertible bond's conversion ratio is
12.5,
and the bond has a par value of
USD 1,000, then each USD 80 of par value can be converted into a
single share. This number is called the
conversion price:
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[1] |
Convertibles routinely have an anti-dilution provision,
which adjusts the conversion ratio as appropriate in the event of a stock
split or stock dividend. Some convertibles have a conversion
ratio that changes according to a fixed schedule. For example, a
convertible bond's
conversion ratio might be 12.5 for the bond's first five years and then drop
to 11 after that.
As is typical of hybrid securities, convertibles can be difficult to
value. Further complicating
valuation, convertibles may have additional embedded
options or
features. Many are callable
after a few years of call
protection.
When called, holders are forced to either surrender the security for the
call price or convert them. If
they convert, the transaction is called a
forced conversion. Some convertibles have a
put feature, allowing holders to
return the security to the issuer for some fraction of par value on
certain dates.
A convertible's
investment value is what the
market value of the convertible
would be if it were stripped of its conversation feature. This reflects the
security's future
cash flows, current interest rates, the issuer's
credit quality, and any
other features such as put or call provisions other than the conversion
option. Investment value isn't
generally observable in the marketplace, but it is a useful notion that
can be ascribed a value using standard bond pricing or
financial engineering methodologies.
A convertible's
conversion value (or parity value)
is the value that could be realized by immediately converting the
convertible to
common stock. It is easily calculated as
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conversion value = (conversion ratio) current stock price |
[2] |
These notions—investment value and conversion value—are
important because a convertible's market price should always exceed both
quantities. Otherwise,
arbitragers will step in and
start accumulating the convertible, thereby driving up its market price.
The two quantities are often quoted as premiums:
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[3] |
| [4] |
Obviously, both premiums should be nonnegative.
Exhibit 1 illustrates how a convertible's market price
depends upon the
underlying stock price. Both the investment
value and conversion value are plotted. The investment value is fairly
flat at higher stock prices but drops off as the stock price falls. This
reflects the fact that the credit quality of the issuer is likely to fall
with a marked decline in the stock price. By [2], the
conversion value is a simple linear function of stock price. The
convertible's market price is also plotted.
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Convertible securities exhibit four different
modes of behavior depending on the level of the underlying stock
price and the credit quality of the issuer. |
Practitioners tend to distinguish between four modes of
behavior of a convertible bond, depending upon the level of the underlying
stock and the issuer's credit quality. Usage is hardly standardized, but
we may distinguish between
distressed,
busted,
hybrid-like,
and
equity-like
modes of behavior. These are also indicated in Exhibit 1.
A convertible's behavior is equity-like when its
conversion value exceeds its investment value, and the bond behaves like
an in-the-money
option. Its value fluctuates almost directly with the underlying stock
price.
The convertible's behavior is hybrid- or option-like at lower
stock prices where the conversion value is less than the investment value
but there is still a reasonable likelihood of the stock price rising
enough to make conversion attractive. In this state, the convertible
exhibit's truly hybrid behavior. Its market price is sensitive to the
underlying stock price, interest rates,
implied volatilities and the
issuer's credit quality.
At still lower stock prices, the conversion option is so
far out of the
money that it is almost worthless. Here, the convertible is
called busted. Its behavior is much like a
non-convertible bond or other fixed income instrument. Its market price
fluctuates with interest rates and the issuer's credit quality.
Finally, if the issuer becomes financially troubled, its
credit rating will fall well below
investment grade and the stock price will plummet to very low levels.
Here the conversion feature is all but irrelevant. The convertible is
a distressed security whose market price fluctuates primarily with the
credit quality of the issuer.
Because convertibles can be so difficult to value, there
is a perception that they are frequently mispriced in the market.
Convertible arbitrage
is a market neutral
trading strategy that seeks to profit from such mispricings.
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