Advanced option topics 1

Volatility Smiles

What is a Volatility Smile? It is the relationship between implied volatility and strike price for options with a certain maturity The volatility smile for European call options should be exactly the same as that for European put options The same is at least approximately true for American options

Why the Volatility Smile is the Same for European Calls and Put Put-call parity p + S 0 e −qT = c +K e –rT holds for market prices (p mkt and c mkt ) and for Black-Scholes-Merton prices (p bs and c bs ) As a result, p mkt − p bs =c mkt − c bs When p bs = p mkt, it must be true that c bs = c mkt It follows that the implied volatility calculated from a European call option should be the same as that calculated from a European put option when both have the same strike price and maturity

The Volatility Smile for Foreign Currency Options (Figure 19.1, page 411) Implied Volatility Strike Price

Implied Distribution for Foreign Currency Options

Properties of Implied Distribution for Foreign Currency Options Both tails are heavier than the lognormal distribution It is also “more peaked” than the lognormal distribution

Possible Causes of Volatility Smile for Foreign Currencies Exchange rate exhibits jumps rather than continuous changes Volatility of exchange rate is stochastic

Historical Analysis of Exchange Rate Changes Real World (%)Normal Model (%) >1 SD >2SD >3SD >4SD >5SD >6SD

The Volatility Smile for Equity Options (Figure 19.3, page 414) Implied Volatility Strike Price

Implied Distribution for Equity Options

Properties of Implied Distribution for Equity Options The left tail is heavier than the lognormal distribution The right tail is less heavy than the lognormal distribution

Reasons for Smile in Equity Options Leverage Crashophobia

Other Volatility Smiles? What is the volatility smile if True distribution has a less heavy left tail and heavier right tail True distribution has both a less heavy left tail and a less heavy right tail

Ways of Characterizing the Volatility Smiles Plot implied volatility against K/S 0 Plot implied volatility against K/F 0 Note: traders frequently define an option as at-the-money when K equals the forward price, F 0, not when it equals the spot price S 0 Plot implied volatility against delta of the option Note: traders sometimes define at-the money as a call with a delta of 0.5 or a put with a delta of −0.5. These are referred to as “50- delta options”

Volatility Term Structure In addition to calculating a volatility smile, traders also calculate a volatility term structure This shows the variation of implied volatility with the time to maturity of the option The volatility term structure tends to be downward sloping when volatility is high and upward sloping when it is low

Volatility Surface The implied volatility as a function of the strike price and time to maturity is known as a volatility surface

Example of a Volatility Surface (Table 19.2, page 417)

Greek Letters If the Black-Scholes price, c BS is expressed as a function of the stock price, S, and the implied volatility,  imp, the delta of a call is Is the delta higher or lower than for equities?

Volatility Smiles When a Large Jump is Expected (pages 418 to 420) At the money implied volatilities are higher that in-the-money or out-of-the-money options (so that the smile is a frown!)

Determining the Implied Distribution (Appendix to Chapter 19)

A Geometric Interpretation (Figure 19A.1, page 425) Assuming that density is g(K) from K−  to K+  c 1 + c 3 − 2c 2 = g(K) e −rT  

Exercises I forgot to include any in the list of recommended ones, so here they are:

Exotics 24

Types of Exotics Packages Nonstandard American options Forward start options Compound options Chooser options Barrier options Binary options Lookback options Shout options Asian options Options to exchange one asset for another Options involving several assets Volatility and Variance swaps etc., etc., etc. 25

Packages Portfolios of standard options Classical spreads and combinations: bull spreads, bear spreads, straddles, etc Often structured to have zero cost One popular package is a range forward contract 26

Forward Start Options Option starts at a future time, T 1 Implicit in employee stock option plans Often structured so that strike price equals asset price at time T 1 27

Forward Start Options Consider this situation: your retail product department asked you for a 2-year maturity capital guaranteed note on the S&P500 stock market index. The note under consideration pays, at the end of the first year, the appreciation of the S&P500 over the previous 12 months and, at the end of the second year, the intervening appreciation of the Eurostoxx50. How would you do this? A forward start option is the forward purchase of a standard call option (i.e. right to buy) or put option (i.e. right to sell). On the forward start date the strike price of the option will be set at a predetermined level. Typically this is the spot price of the asset on the forward start date (i.e. at-the-money), alternatively the strike price can be set at a percentage in or out of the money (i.e. a percentage above or below the current spot price of the asset).

‘Ratchet’ Options Forward Start Options are often combined in a series into a Ratchet Option (also called ‘cliquet’ or reset options) with each option commencing with an at-the-money strike when the previous option expires.  The result of this is a single option which allows the investor to lock in profits over the life of the option.

Compound Option Option to buy or sell an option  Call on call  Put on call  Call on put  Put on put Price is quite low compared with a regular option 30

Barrier Options Option comes into existence only if stock price hits barrier before option maturity  ‘In’ options Option dies if stock price hits barrier before option maturity  ‘Out’ options 31

Barrier Options (continued) Stock price must hit barrier from below  ‘Up’ options Stock price must hit barrier from above  ‘Down’ options Option may be a put or a call Eight possible combinations 32

Parity Relations c = c ui + c uo c = c di + c do p = p ui + p uo p = p di + p do 33

Binary Options Cash-or-nothing: pays Q if S T > K, otherwise pays nothing. Value according to B&S = e –rT Q N(d 2 ) Asset-or-nothing: pays S T if S T > K, otherwise pays nothing. Value according to B&S = S 0 e -qT N(d 1 ) 34

Decomposition of a Call Option Long Asset-or-Nothing option Short Cash-or-Nothing option where payoff is K Value according to B&S = S 0 e -qT N(d 1 ) – e –rT KN(d 2 ) 35

Asian Options Payoff related to average stock price Average Price options pay:  Call: max(S ave – K, 0)  Put: max(K – S ave, 0) Average Strike options pay:  Call: max(S T – S ave, 0)  Put: max(S ave – S T, 0) 36

Asian vs. Plain Vanilla Options (C – P) av price + (C – P) av strike   max(0, S av – K) – max(0,K - S av ) + max(0,S T - S av ) – max(0,S av - S T )  max(0, S av – K + S T - S av ) – {max(0, K - S av ) + max(0, S av - S T )}  max(0, S av – K + S T - S av ) – {max(0, K – S av + S av – S T )}  max(0, S T – K) – {max(0, K – S T )}  C – P 37

Basket Options A basket option is an option to buy or sell a portfolio of assets Not the same as a basket of options, it entails a position on both the volatility AND the correlation of the underlying assets 38

Volatility and Variance Swaps Volatility swap is agreement to exchange the realized volatility between time 0 and time T for a prespecified fixed volatility with both being multiplied by a prespecified principal Variance swap is agreement to exchange the realized variance rate between time 0 and time T for a prespecified fixed variance rate with both being multiplied by a prespecified principal. Daily return is assumed to be zero in calculating the volatility or variance rate

VIX Index (page 590) The RN expected value of the variance of the S&P 500 over 30 days is calculated from the CBOE market prices of European put and call options on the S&P 500. This is then multiplied by 365/30 and the VIX index is set equal to the square root of the result

………etc, etc….

How Difficult is it to Hedge Exotic Options? In some cases exotic options are easier to hedge than the corresponding vanilla options (e.g., Asian options) In other cases they are more difficult to hedge (e.g., barrier options)

Static Options Replication This involves approximately replicating an exotic option with a portfolio of vanilla options Underlying principle: if we match the value of an exotic option on some boundary, we have matched it at all interior points of the boundary Static options replication can be contrasted with dynamic options replication where we have to trade continuously to match the option Further details and example in appendix/textbook

Appendix

Expected variance for variance swap valuation The (risk-neutral) expected variance rate between times 0 and T can be calculated from the prices of European call and put options with different strikes and maturity T For any value of S *

Volatility Swap For a volatility swap it is necessary to use the approximate relation

Non-Standard American Options Exercisable only on specific dates (Bermudans) Early exercise allowed during only part of life (initial “lock out” period) Strike price changes over the life (warrants, convertibles)

Exchange Options Option to exchange one asset for another For example, an option to exchange one unit of U for one unit of V Payoff is max(V T – U T, 0) 48

Lookback Options Floating lookback call pays S T – S min at time T (Allows buyer to buy stock at lowest observed price in some interval of time) Floating lookback put pays S max – S T at time T (Allows buyer to sell stock at highest observed price in some interval of time) Fixed lookback call pays max(S max −K, 0) Fixed lookback put pays max(K −S min, 0)

Shout Options Buyer can ‘shout’ once during option life Final payoff is either  Usual option payoff, max(S T – K, 0), or  Intrinsic value at time of shout, S  – K Payoff: max(S T – S , 0) + S  – K Similar to lookback option but cheaper

Example A 9-month up-and-out call option an a non- dividend paying stock where S 0 = 50, K = 50, the barrier is 60, r = 10%, and  = 30% Any boundary can be chosen but the natural one is c ( S, 0.75) = max( S – 50, 0) when S  60 c (60, t ) = 0 when 0  t  0.75

The Boundary

Example (continued) We might try to match the following points on the boundary c(S, 0.75) = MAX(S – 50, 0) for S  60 c(60, 0.50) = 0 c(60, 0.25) = 0 c(60, 0.00) = 0

Example continued (See Table 25.1, page 593) We can do this as follows: call with maturity 0.75 & strike 50 –2.66 call with maturity 0.75 & strike call with maturity 0.50 & strike call with maturity 0.25 & strike 60

Example (continued) This portfolio is worth 0.73 at time zero compared with 0.31 for the up-and out option As we use more options the value of the replicating portfolio converges to the value of the exotic option For example, with 18 points matched on the horizontal boundary the value of the replicating portfolio reduces to 0.38; with 100 points being matched it reduces to 0.32

Using Static Option Replication To hedge an exotic option we short the portfolio that replicates the boundary conditions The portfolio must be unwound when any part of the boundary is reached

How Difficult is it to Hedge Exotic Options? In some cases exotic options are easier to hedge than the corresponding vanilla options (e.g., Asian options) In other cases they are more difficult to hedge (e.g., barrier options)