Equity Options (Part 1)

15.433 INVESTMENTS Class 10: Equity Options Part 1: Pricing Spring 2003 SPX S&P 500 Index Options Symbol: SPX Underlying: The Standard & Poor’s 500 Index is a capitalizationweighted index of 500 stocks from a broad range of industries. The component stocks are weighted according to the total market value of their out-standing shares. The impact of a component’s price change is proportional to the issue’s total market value, which is the share price times the number of shares out-standing. These are summed for all 500 stocks and divided by a predetermined base value. The base value for the S&P 500 Index is adjusted to reflect changes in capitalization resulting from mergers, acquisitions, stock rights, substitutions, etc. Multiplier: $100. Strike Price Intervals: Five points. 25-point intervals for far months. Strike (Exercise) Prices: In-,at- and out-of-the-money strike prices are initially listed. New series are generally added when the underlying trades through the highest or lowest strike price available. Premium Quotation: Stated in decimals. One point equals $100. Minimum tick for options trading below 3.00 is 0.05 ($5.00) and for all other series, 0.10 ($10.00). Expiration Date: Saturday immediately following the third Friday of the expiration month. Expiration Months: Three near-term months followed by three additional months from the March quarterly cycle (March, June, September and December). Exercise Style: European - SPX options generally may be exercised only on the last business day be-fore expiration. Settlement of Option Exercise: The exercise-settlement value, SET, is calculated using the opening (first) reported sales price in the primary market of each component stock on the last business day (usually a Friday) before the expiration date. If a stock in the index does not open on the day on which the exercise & settlement value is determined, the last reported sales price in the primary market will be used in calculating the exercise-settlement value. The exercise-settlement amount is equal to the difference between the exercise-settlement value, SET, and the exercise price of the option, multiplied by $100. Exercise will result in delivery of cash on the business day following expiration. Position and Exercise Limits: No position and exercise limits are in effect. Each member (other than a market-maker) or member organization that maintains an end of day position in excess of 100,000 contracts in SPX (10 SPX LEAPS equals 1 SPX full value contract) for its proprietary account or for the account of a customer, shall report certain information to the Department of Market Regulation. The member must report information as to whether such position is hedged and, if so, a description of the hedge employed. A report must be filed when an account initially meets the aforementioned applicable threshold. Thereafter, a report must be filed for each incremental increase of 25,000 contracts. Reductions in an options position do not need to be reported. However, any significant change to the hedge must be reported. Margin: Purchases of puts or calls with 9 months or less until expiration must be paid for in full. Writers of uncovered puts or calls must deposit / maintain 100CUSIP Number: 648815 Last Trading Day: Trading in SPX options will ordinarily cease on the business day (usually a Thursday) preceding the day on which the exercise-settlement value is calculated. Trading Hours: 8:30 a.m.- 3:15 p.m. Central Time (Chicago time). Equity Options: The Basics A European style call option is the right to purchase, on a future date T, one unit of the underlying asset at a pre determined price K: • At time 0 (today), pay C. • At time T (the expiration date), exercise the option and get (ST − K)+. A put option gives the right to sell: • At time 0 (today), pay P. • At time T, get (K − ST )+. Most of the index options (e.g., SPX, QEX, NDX) are European style. All of the options on the individual stocks are American style, which allow for exercise before the expiration date T. S&P 500 Options .SPX (CBOE),1118.49,-1.82, Nov 12 2001 @ 15:27 ET (Data 15 Minutes Delayed), Calls Last Sale Net 02 Mar 750.0 (SPZ CJ-E) 318.40 pc 02 Mar 775.0 (SPZ CO-E) pc 02 Mar 800.0 (SPX CT-E) pc 02 Mar 850.0 (SPX CJ-E) pc 02 Mar 900.0 (SXB CT-E) 189.00 pc Bid 370.10 346.20 322.30 275.50 229.80 Ask 374.10 350.20 326.30 279.50 233.80 Vol - 02 Mar 925.0 (SXB CE-E) 02 Mar 950.0 (SXB CJ-E) 02 Mar 975.0 (SXB CO-E) 02 Mar 995.0 (SXB CS-E) 02 Mar 1025. (SPQ CE-E) 02 Mar 1050. (SPQ CJ-E) 02 Mar 1075. (SPQ CO-E) 02 Mar 1100. (SPT CT-E) 02 Mar 1125. (SPT CE-E) 02 Mar 1150. (SPT CJ-E) 02 Mar 1175. (SPT CO-E) 02 Mar 1200. (SZP CT-E) 02 Mar 1225. (SZP CE-E) 02 Mar 1250. (SZP CJ-E) 02 Mar 1275. (SZP CO-E) 02 Mar 1280. (SZP CP-E) 02 Mar 1300. (SXY CT-E) 02 Mar 1325. (SXY CE-E) 02 Mar 1350. (SXY CJ-E) 02 Mar 1375. (SXY CO-E) 02 Mar 1400. (SXZ CT-E) 02 Mar 1425. (SXZ CE-E) 02 Mar 1450. (SXZ CJ-E) 02 Mar 1475. (SXZ CO-E) 02 Mar 1500. (SXM CT-E) 02 Mar 1550. (SXM CJ-E) 02 Mar 1600. (SPB CT-E) 02 Apr 1020. (SYU DD-E) 02 Jun 700.0 (SPZ FT-E) 02 Jun 725.0 (SPZ FE-E) 02 Jun 750.0 (SPZ FJ-E) 02 Jun 800.0 (SPX FT-E) 02 Jun 850.0 (SPX FJ-E) 02 Jun 900.0 (SXB FT-E) 02 Jun 950.0 (SXB FJ-E) 02 Jun 995.0 (SXB FS-E) 02 Jun 1025. (SPQ FE-E) 02 Jun 1045. (SPQ FI-E) 02 Jun 1050. (SPQ FJ-E) 02 Jun 1075. (SPQ FO-E) 02 Jun 1100. (SPT FT-E) 02 Jun 1125. (SPT FE-E) 02 Jun 1150. (SPT FJ-E) 02 Jun 1175. (SPT FO-E) 02 Jun 1200. (SZP FT-E) 02 Jun 1225. (SZP FE-E) 144.90 153.00 148.00 94.00 108.00 80.00 72.00 53.00 47.40 29.50 21.00 19.00 16.50 8.50 6.30 5.40 5.00 3.50 1.30 1.00 0.80 0.35 2.00 0.50 0.50 0.55 225.00 161.50 164.00 121.00 115.00 108.50 91.30 79.00 61.00 54.00 46.50 35.50 pc pc 61.00 pc pc 2.50 (14.00) (1.00) (6.00) pc (7.50) (5.30) pc pc 2.50 pc pc pc pc pc pc pc pc pc pc pc pc pc pc pc pc pc pc pc pc pc pc pc (10.30) pc (3.00) pc (6.00) pc pc pc 207.40 185.70 164.40 148.00 124.80 106.20 88.80 72.30 57.50 44.80 33.70 24.50 17.60 11.80 8.00 7.30 5.00 3.10 1.90 1.00 0.45 0.05 420.80 397.40 374.00 327.70 282.80 239.30 197.80 162.60 140.50 123.10 106.70 91.60 77.60 64.80 53.10 42.40 33.90 211.40 189.70 168.40 152.00 128.80 110.20 92.80 76.30 61.50 48.80 37.70 28.50 20.60 14.80 10.00 9.30 6.40 4.50 2.80 1.90 1.30 0.95 0.90 0.90 0.90 0.90 0.90 424.80 401.40 378.00 331.70 286.80 243.30 201.80 166.60 144.50 127.10 110.70 95.60 81.60 68.80 57.10 46.40 37.90 2.00 4.00 2.00 560.00 1.00 3.00 3.00 1.00 5.00 401.00 5.00 - 1,078 2 2,109 1,818 8,059 3,929 13,293 7,351 8,354 3,148 13,211 3,922 10,727 3,035 3 6,073 2,241 4,957 789 8,718 269 1,986 94 1,173 28 931 121 28 2,670 1,358 1,350 3,393 1,186 5,411 1,885 5,415 673 7,255 1,451 02 Mar 925.0 (SXB OE-E) 02 Mar 950.0 (SXB OJ-E) 02 Mar 975.0 (SXB OO-E) 02 Mar 995.0 (SXB OS-E) 02 Mar 1025. (SPQ OE-E) 02 Mar 1050. (SPQ OJ-E) 02 Mar 1075. (SPQ OO-E) 02 Mar 1100. (SPT OT-E) 02 Mar 1125. (SPT OE-E) 02 Mar 1150. (SPT OJ-E) 02 Mar 1175. (SPT OO-E) 02 Mar 1200. (SZP OT-E) 02 Mar 1225. (SZP OE-E) 02 Mar 1250. (SZP OJ-E) 02 Mar 1275. (SZP OO-E) 02 Mar 1280. (SZP OP-E) 02 Mar 1300. (SXY OT-E) 02 Mar 1325. (SXY OE-E) 02 Mar 1350. (SXY OJ-E) 02 Mar 1375. (SXY OO-E) 02 Mar 1400. (SXZ OT-E) 02 Mar 1425. (SXZ OE-E) 02 Mar 1450. (SXZ OJ-E) 02 Mar 1475. (SXZ OO-E) 02 Mar 1500. (SXM OT-E) 02 Mar 1550. (SXM OJ-E) 02 Mar 1600. (SPB OT-E) 02 Apr 1020. (SYU PD-E) 02 Jun 700.0 (SPZ RT-E) 02 Jun 725.0 (SPZ RE-E) 02 Jun 750.0 (SPZ RJ-E) 02 Jun 800.0 (SPX RT-E) 02 Jun 850.0 (SPX RJ-E) 02 Jun 900.0 (SXB RT-E) 02 Jun 950.0 (SXB RJ-E) 02 Jun 995.0 (SXB RS-E) 02 Jun 1025. (SPQ RE-E) 02 Jun 1045. (SPQ RI-E) 02 Jun 1050. (SPQ RJ-E) 02 Jun 1075. (SPQ RO-E) 02 Jun 1100. (SPT RT-E) 02 Jun 1125. (SPT RE-E) 02 Jun 1150. (SPT RJ-E) 02 Jun 1175. (SPT RO-E) 02 Jun 1200. (SZP RT-E) 02 Jun 1225. (SZP RE-E) 02 Jun 1250. (SZP FJ-E) 02 Jun 1300. (SXY FT-E) 02 Jun 1325. (SXY FE-E) 02 Jun 1350. (SXY FJ-E) 02 Jun 1375. (SXY FO-E) 02 Jun 1400. (SXZ FT-E) 02 Jun 1425. (SXZ FE-E) 02 Jun 1450. (SXZ FJ-E) 02 Jun 1475. (SXZ FO-E) 02 Jun 1500. (SXM FT-E) 02 Jun 1525. (SXM FE-E) 27.50 17.50 11.20 7.00 6.00 4.00 1.80 2.20 1.90 1.20 0.90 pc pc pc (1.00) pc -pc pc pc pc pc 26.20 15.00 10.80 8.10 5.60 4.00 2.90 1.90 1.25 0.60 0.25 30.20 18.00 13.80 10.10 7.60 5.40 3.90 2.80 2.15 1.50 1.15 11.00 10.00 - 6,959 7,065 1,469 5,481 787 12,350 329 8,703 123 8,537 320 02 Jun 1550. (SXM FG-E) 02 Jun 1550. (SXM FJ-E) 02 Jun 1600. (SPB FT-E) 02 Jun 1650. (SPB FJ-E) 02 Jun 1700. (SPV FT-E) 02 Jun 1750. (SPV FJ-E) 02 Jun 1800. (SYV FT-E) 0.30 0.40 2.90 0.10 0.65 0.05 0.10 - 0.95 0.90 0.90 0.90 0.90 0.90 5.00 - 3,458 6,212 3,849 3,439 1,120 4,132 pc -pc pc pc pc pc Figure 2: Source: www.cboe.com Open Int Puts 32 02 Mar 750.0 (SPZ OJ-E) 02 Mar 775.0 (SPZ OO-E) 02 Mar 800.0 (SPX OT-E) 02 Mar 850.0 (SPX OJ-E) 51 02 Mar 900.0 (SXB OT-E) Last Sale 4.80 4.00 5.00 9.00 12.50 Net 1.10 pc pc 1.50 1.10 Bid 3.10 4.00 5.00 7.40 10.90 Ask 4.50 5.30 6.30 9.40 13.80 Vol 1.00 3.00 7.00 Open Int 13,629 12,283 6,600 3,801 13,075 23.00 17.00 25.00 24.00 32.20 40.00 48.80 55.00 70.00 79.00 93.00 97.60 140.00 143.00 193.00 72.50 195.00 328.00 250.50 276.00 290.00 344.00 343.00 408.50 7.40 11.00 7.30 10.00 14.50 19.50 29.00 37.50 44.00 52.00 66.40 76.00 84.50 103.00 86.00 150.00 179.50 pc pc pc 0.60 2.20 3.50 6.50 4.00 8.00 5.00 pc pc 18.00 (15.00) pc pc 16.80 pc pc pc 19.00 pc pc pc pc pc pc pc pc pc pc pc pc pc (1.00) pc pc pc pc 6.40 6.00 3.50 pc pc pc pc 13.20 16.30 19.70 22.80 28.80 35.10 42.40 51.00 62.00 73.00 86.70 102.80 120.20 139.10 159.60 163.70 181.10 203.80 227.20 251.10 275.30 299.70 324.30 349.10 373.90 423.30 472.90 4.50 5.40 6.70 9.70 13.50 19.30 26.60 35.70 43.20 50.40 58.60 68.20 78.80 90.60 103.60 117.50 133.60 16.20 19.30 22.70 26.80 32.80 39.00 46.40 55.00 64.90 77.00 90.70 106.80 124.20 143.10 163.60 167.70 185.10 207.80 231.20 255.10 279.30 303.70 328.30 353.10 377.90 427.30 476.90 5.90 7.40 8.70 11.70 16.50 22.30 30.60 39.70 47.20 54.40 62.60 72.20 82.80 94.60 107.60 121.50 137.60 2.00 110.00 626.00 101.00 103.00 436.00 1.00 5.00 1.00 200.00 200.00 3.00 2.00 10.00 3.00 - 633 7,719 3,991 11,110 9,778 8,300 4,833 5,684 3,239 9,298 4,549 8,920 3,514 4,579 1,080 2 2,007 213 918 266 1,230 679 60 55 734 14 1,064 2,852 2,993 6,983 4,332 9,137 6,127 1,350 12,129 1,144 14,313 1,412 5,536 160 6,462 446 02 Jun 1250. (SZP RJ-E) 02 Jun 1300. (SXY RT-E) 02 Jun 1325. (SXY RE-E) 02 Jun 1350. (SXY RJ-E) 02 Jun 1375. (SXY RO-E) 02 Jun 1400. (SXZ RT-E) 02 Jun 1425. (SXZ RE-E) 02 Jun 1450. (SXZ RJ-E) 02 Jun 1475. (SXZ RO-E) 02 Jun 1500. (SXM RT-E) 02 Jun 1525. (SXM RE-E) 153.00 244.90 227.00 248.00 280.00 290.00 388.00 396.00 347.00 pc pc pc pc pc 1.00 pc pc pc pc pc 150.60 188.20 208.70 230.10 252.20 275.00 298.20 321.90 345.90 369.80 394.10 154.60 192.20 212.70 234.10 256.20 279.00 302.20 325.90 349.90 373.80 398.10 200.00 - 2,280 4,474 152 2,724 5 5,677 3,946 2,882 101 02 Jun 1550. (SXM RG-E) 02 Jun 1550. (SXM RJ-E) 02 Jun 1600. (SPB RT-E) 02 Jun 1650. (SPB RJ-E) 02 Jun 1700. (SPV RT-E) 02 Jun 1750. (SPV RJ-E) 02 Jun 1800. (SYV RT-E) 417.00 302.00 513.00 590.00 724.70 811.00 pc pc pc pc pc pc pc 418.60 467.60 516.80 566.00 615.20 664.50 422.60 471.60 520.80 570.00 619.20 668.50 - 1,622 944 350 248 43 596 The Value of a Call Option max[0,S(T)-K] Payoff in $ Payoff in $ K Terminal Spot Price, S(T) 0 0 Terminal Spot Price, S(T) K - max [0, S(T) - K] Figure 3: Value of a Long Call Figure 4: Value of Short Call at Expiration at Expiration Notice that the short call option payoff is unbounded from below. Payoff in $ max [0, K - S(T)] Payoff in $ K Terminal Spot Price, S(T) 0 0 Terminal Spot Price, S(T) K -K Figure 5: Value of a Long Put at Expiration - max [0, K - S(T)] Figure 6: Value of a Short Put at Expiration Hence you can buy a put option if you are a pessimist, i.e., you have a hunch, but are not absolutely certain, about the stock price, S, going below the strike price, K, at maturity (for Euro-pean options). Notice that the long put option payoff is bounded above by K. Option Pricing ”Suppose the underlying security does not pay dividend, rT = ln (ST ) − ln (SO ) (1) � � S0 = E e−ri,T · ST (2) or equivalently: A call option paying (ST − K)+ at time T must be worth: � � C0 = E e−ri,T · (ST − K)+ (3) From the intuition of the CAPM, we know that the above evaluation depends on the risk aversion coefficient A of the representative investor. ”For example, if the underlying asset is the market portfolio, then E (rT ) − rf = Ā · var (rT ) (4) The question is: how to evaluate � � C0 = E e−ri,T · (ST − K)+ (5) Single Period Binominal-Valuation Problem Suppose that a European call option struck at $ 50 matures in one year (t = 1). The riskless rate per year is 25%, compounded annually, so that one dollar invested at the riskless rate grows to $ 1.25 over the year. The stock underlying the option pays no dividends over the year and its current price of $ 40 will either double or halve over the year. Assuming frictionless markets and no arbitrage, what must be the current price of the call, C0 ? • Strike Price of the call = K = $ 50 • Riskless return over the period = R(1) = 1.25 • Unit Bond price = B(0, 1) = 1 1.25 = $0.80 • Stock price at the beginning of the period = S0 = $40 • Up return of the stock = U = 2 • Down return of the stock = D = 1 2 • Call value at the end of the period given an Up return of the stock = CU = max[0, S0 · U − K] = $30 • Call value at the end of the period given a down return of the stock = CD = max[0, S0 · D − K] = $0 • Call value at the beginning of the period = C0 =? (Ans: $ 12. The next section will derive the price). Spanning the Payoffs Consider a portfolio of m0 shares of the underlying stock and B0 dollars invested in the riskless asset, Assume you form the portfolio at time 0. The portfolio has two possible values at the end of the period, depending on whether the stock price goes up or down: U p : m0 · 80 + B0 · 1.25 (6) Down : m0 · 20 + B0 · 1.25 (7) Similarly, the call value has two possible values: Up: 30 or Down: 0 We can choose the number of shares, m0 , and the amount invested in the riskless asset, B0 , today, so that the value of the stock-bond portfolio equates to the value of the call next year: 1. m0 · 80 + B0 · 1.25 = 30 2. m0 · 20 + B0 · 1.25 = 0 Subtracting (2) from (1) and solving for the number of shares, m0 , we get m0 = 30 − 0 1 = 80 − 20 2 (8) Plugging for m0 into either (1) or (2), we get B0 = −8$. The minus sign for B0 means we have to borrow $8 at the riskless rate. Valuation Since buying 1 2 of a share of the stock and shorting $8 of the risk-less asset duplicates the payoff of the all, avoiding arbitrage requires that the current price of the traded call equals the cost of duplicating it. Hence, the current call value is: V (0) = 12 · $40 − $8 = $12. Remarks: • The required number of shares, m0 = 12 , is the difference in next year’s possible call values, expressed as a proportion of the difference in next year’s possible stock prices: m0 = 30 − 0 1 = 80 − 20 2 (9) • For a European call option, the required number of shares is always between 0 and 1. In a graph of call values against stock prices, the required number of shares is the slope of the graph. For this reason, the required number of shares is often called the delta of the call. Delta is the sensitivity of the call option price to stock price changes. It is a very useful parameter in hedging. The amount invested in the riskless asset is negative (B0 = −$8). Consequently, the riskless bond must be shorted. Short selling bonds is equivalent to borrowing. The amount to be repaid at the end of the period is (B0 · 1.25) = $10, irrespective of being in the up state or down state. • This approach can be used in a binomial framework to value any claim whose payoff is contingent on the price of the stock (e.g., a put). • Notice that the probabilities q and 1−q do not enter the valuation argument at all. Hence, 2 individuals who disagree about the probabilities of outcomes (q, 1 − q), but who agree on the outcomes (i.e., U and D), will agree that the traded option’s value today is 12. • Since we assume that the stock can only take on two values from any node, we only need two assets (the underlyer and the riskless asset) to replicate the payoff of the option. Any additional uncertainty (example, stochastic interest rates) would require additional assets. Fisher Black on Option Pricing ”I applied the Capital Asset Pricing Model to every moment in a warrant’s life, for every possible stock price and warrant value ... I stared at the differential equation for many, many months. I made hundreds of silly mistakes that led me down blind alleys. Nothing worked . . . [The calculations revealed that] the warrant value did not depend on the stock’s ex­ pected return, or on any other asset’s expected return. That fascinated me. [He adds:] Then Myron-Scholes and I started working together”. Risk Neutral Pricing It turns out that Black was not far from the truth! • Two hypothetical investors: one risk neutral (A = 0), and one risk averse (A > 0). • Suppose both investors are willing to pay the market price S0 for the underlying asset. But their required rates of return are different: – For the risk neutral investor, it is simply the riskfree rate rf . – For the risk averse, it is the riskfree rate rf plus a positive risk premium. • If they agreed on So, they would also agree on C0 for the call. If this is true, the easiest way to get C0 is to let the risk neutral investor do the pricing. Hence the term ”risk neutral pricing.” One key assumption: All investors, regardless of their risk attitudes, agree on today’s stock price S0 . Risk-Neutral Valuation Risk neutral valuation is a trick for valuing options quickly when investors can be riskaverse. It is not a model which assumes investors are all risk-neutral. Recall that the version of the binomial model we studied assumed frictionless markets, no arbitrage, European options, a constant riskless rate, no payouts, and a multiplicative binomial process for the underlyer’s spot price. We were able to value a European call and put without any knowledge of investor preferences or beliefs regarding the likelihood of the up or down states. This is called Valuation by Duplication. Since the same value results regardless of investor preferences, we can pretend that investors are risk-neutral as an aid in calculating values. In this case, the expected return on the underlyer is the riskless return rf . Letting π denote the risk-neutral probability of an up jump, we have: St = 1 · [π · St · U + (1 − π) · St · D] rf (10) implying π · U + (1 − π) · D = rf (11) or equivalently rf − D U −D Under risk-neutrality, the expected payoff of a 1-period call is: π= − c+ 1 = (1 − π) · c1 (12) (13) where recall: � � + c+ 1 = max 0, S1 − K is the call value in the up state � � − c− 1 = max 0, S1 − K is the call value in the down state π= rf −D U −D is the risk-neutral probability of an up jump found by equating the expected return from the underlying to the riskless return. In a risk-neutral world, the expected return on an option is also the riskless return. Thus, the initial call value c0 is given by discounting the above expected payoff at the riskless return rf : � � − c0 = rf−1 · π · c+ 1 + (1 − π) · c1 (14) Valuation by Duplication is the reason why risk-neutral valuation works. The same idea can be used for puts and for multiple periods. Risk-neutral valuation permits very quick calculation of option values. Risk-neutral valuation, hence, simplifies the valuation problem (compared to valuation by duplication which was mighty cumbersome for multiple periods). Furthermore, the composition of the duplicating portfolio is easily calculated once the option values are known. Armed with the risk-neutral probabilities π and 1 − π, we can duplicate and price anything. For example, to duplicate a contingent claim paying XU dollars if the spot price goes up and XD dollars if the spot price goes down, we use risk-neutral valuation to calculate the current price of the contingent claim as: rf−1 · [π · XU + (1 − π) · XD ] (15) which is interpreted as the discounted expected payoff under risk-neutrality. Example: Recall (see previous page) for 1-period calls, � � − c0 = rf−1 · π · c+ 1 + (1 − π) · c1 (16) where XU = C1+ and XD = C1− . If we think of XU and XD as option values in successor nodes, then we have a recipe for valuing in multiple periods as illustrated next. Note: The risk neutral probabilities π and 1 − π are usually referred to also as the equivalent martingale probabilities. Two Period Example Given T = 2, S0 = 40, U = 2, D = 1 ,r 2 f = 5 , 4 K = 50, what is the risk-neutral probability of an up jump? 5 − 12 rf − D 1 4 π= = 1 = 2 U −D 2− 2 (17) Use risk-neutral valuation to calculate the values of a call at each node bow. Also give the number of stocks and the amount lent in order to replicate the call value at each node. Compare your answers with those obtained using the method of replication (see 2-period example in Section 3 of Overheads 3). + 160 80 + c1 40 40 c2 0 c0 c2 - 20 c1 10 Figure 7 : Two period binomial Figure 8: Two period binomial tree, call option tree, call option - c2 − 0 Answer: Note that c+ 2 = max[0, 160 − 50] = 110, while c2 = c2 = 0$. c+ 1 c− 1 c0 � � 1 1 1 = · · 110 + · 0 2 2 rf = 0 � � 1 1 + 1 − = · · c + · c1 rf 2 1 2 (18) (19) (20) (21) The call’s Delta and the amount lent at each node is given by: 0 c+ 11 2 − c2 = + 0 12 S2 − S 2 + 0 0 + 1 c S −c S = 2 � 2 + 2 02� = −29 3 rf S 2 − S 2 m+ = 1 (22) B1+ (23) 0 c+ 11 1 − c1 = + 0 15 S1 − S 1 + 0 0 + 11 c S −c S = 1 � 1 + 1 01� = −11 15 rf S 1 − S 1 m0 = (24) B0 (25) Use risk-neutral valuation to calculate the values of a put at each node bow. Also give the number of stocks and the amount lent in order to replicate the put value at each node. + 160 80 40 + p1 0 p0 40 p2 p2 - p1 20 10 Figure 9: Two period binomial Figure 10: Two period binomial tree, put option tree, put option - p2 0 Answer: Note that p− 2 = max[0, 50 − 10] = $40, while p2 = max[0, 50 − 40] = $10 and p+ 2 = 0. Therefore, p+ 1 p− 1 p0 1 = rf 1 = rf 1 = rf � � 1 1 · · 10 + · 0 = $4 2 2 � � 1 1 · · 10 + · 40 = $20 2 2 � � 1 + 1 − · · p + · p1 = $9.60 2 1 2 (26) (27) (28) We can use Put-Call Parity to check whether our answers make sense. Recall p0 + S0 = c0 + K · B(0, 2). LHS = p0 + S0 = 9.60 + 40 = $49.60. RHS = c0 + K · B(0, 2) = $17.60 + $32 = $49.60. What is the Intuition? If there is only one source of uncertainty in the underlying stock, then the effect of the random shock is fully reflected in the underlying stock price. In such a setting, option becomes redundant. Investors are risk averse: they are worried about the systematic random fluctuations in the stock price. This fear is fully ex-pressed when investors price the underlying security. When it comes to price options, investors are already at a comfortable level regarding risk and reward. Options, being redundant in this setting, provide no additional information about the risk or the reward. There is no assumption about investors being risk neutral. Risk neutral pricing is a trick to simplify option pricing. The Assumptions 1. Constant riskfree borrowing and lend rate rf . 2. The underlying asset can be continuously traded with no transactions costs, no short sale constraints, perfectly divisible, and no taxes. 3. We assume no dividends, but this restriction can be relaxed. 4. The price of the underlying asset follows a Geometric Brownian Motion: dSt = µ · dt + σ · dBt St (29) This model is the continuous time version of the random walk model we have studied in Class 9. The increment ∆Bt of a Brownian motion is normally distributed with mean zero and variance ∆t. The Black Scholes Formula A European call struck at K, expiring on date T. C0 = S0 · N (d1 ) − e−rT KN (d2 ) (30) where � + rf + K √ d1 = σ· T � � � ln SK0 + rf − √ d2 = σ· T ln � S0 � σ2 2 σ2 2 � � ·T ·T (31) (32) and where • S0 is the initial stock price, • σ is its volatility • rf is the riskfree rate N (dx ) is the probability that the outcome of a standard normal distribution is less than d. Put/Call Parity c − p = Stz − K · B (t, T ) (33) = max [0, Stz − K · B (t, T )] − max [0, K · B(t, T ) − Stz ] . (34) c − p = S − e−r(T −T ) · K put − call parity The value of the call minus the value for the put is equal to the value for the stock minus the present value of K. We have two investments: 1. Buy the call option and sell the put option. Value: c − p 2. Go long the stock and sell a riskless, zero-coupon bond maturing at time T to K. Value: S − e−r(T −t) · K Neither of these instruments incur any costs during their lifetime. Let‘s examine their values at time T, starting with investment one, the long-call, short-put investment. Since the call and the put have the same strike, at expiration either the call will be in the money or the put will be in the money - but never both. Write ST for the value for the stock at time T. If the call is in the money, the payoff is ST − K, since the position is long. On the other hand, if the short put is in the money, the its payoff is −(K − ST ) = ST − K. That is, since the position is short, its payoff is the negative of the usual K − ST , independent of the stock price at Time T. The second investment, the stock-bond portfolio is comparatively easy to value. At time T, the bond will have matured to a value of K, and therefore the long-stock, short-bond position will have a value of ST − K. Both investments have the same value at time T, and moreover, cost nothing to maintain. Therefore, our basic arbitrage argument tells us the investments must have the same initial value, that is: c−p � �� � value of investment 1 = −r(T −t) · K� S � − e �� value of investment 2 (35) Reflections of Volatility Option Price (S) in-the-money at-the-money out-of-the-money Volatility (σ) Figure 11: Volatility-levels for in, at or out-of-the-money options. 100 90 80 70 60 50 40 30 20 vxn 7/2/2001 1/2/2001 7/2/2000 1/2/2000 7/2/1999 1/2/1999 7/2/1998 1/2/1998 7/2/1997 1/2/1997 7/2/1996 1/2/1996 7/2/1995 1/2/1995 7/2/1994 1/2/1994 7/2/1993 1/2/1993 7/2/1992 1/2/1992 7/2/1991 0 1/2/1991 10 vix Figure 12: Distribution of the Nasdaq-index returns for the year 2000, data-source: Bloomberg. VXN is based on the implied volatility of the Nasdaq-100 (NDX) options, while the VIX volatility is based on the implied volatilities of the S&P 100-OEX options. The Options Market and Volatility A casual inspection of the options market leads one to believe that stock volatility does not stay constant over time. Why? Investors express their view on the future market volatility by trading options. Effectively, the equity options market serves as an information central, collecting updates about the future market volatility: • short dated options: near term volatility; • long dated options: long term volatility. 100 1400 90 1200 80 1000 70 800 60 50 600 40 400 30 20 200 10 0 NDX 7/2/1997 1/2/1997 7/2/1996 1/2/1996 7/2/1995 1/2/1995 7/2/1994 1/2/1994 7/2/1993 1/2/1993 7/2/1992 1/2/1992 7/2/1991 1/2/1991 0 VXN Figure 13: VXN: Impl. volatility of options on the NDX; NDX: Impl. volatility of Nasdaq-100 index, datasource: Bloomberg Professional. Important: VXN and NDX can have somewhat negative correlations! The Option Implied Volatility At time 0, a call option struck at K and expiring on date T is traded at C0 . At the same time, the underlying stock price is traded at S0 , and the riskfree rate is rf . If we know the market volatility at time 0, we can apply the Black Scholes formula: 0 = BS (S0 , K, T, σ, rf ) CBS (36) Volatility is something that we don’t observe directly. But using the market observed price C0 , we can back it out: � � C0 = BS S0 , K, T, σ I , rf (37) If the Black Scholes model is the correct model, then the Option Implied Volatility σ I should be exactly the same as the true volatility σ. Why Options? Hedging, (speculative) investing, and asset allocation are among the top reasons for option trading. In essence, options and other derivatives provide a tailored service of risk by slicing, reshaping, and re packaging the existing risks in the underlying security. The risks are still the same, but investors can choose to take on different aspects of the existing risks in the underlying asset. Reasons Institutions, Use Equity Derivatives 0% 10% 20% 30% 40% 50% Investing 44% 42% Asset Allocation Indexing 40% Market Timing 26% International Access Riasing Cash (e.g. to cover redemption) Tax Minimization 70% 61% Hedging Tailoring Cash Flow 60% 25% 14% 13% 10% Figure 14: Reasons Institutions, Use Equity Derivatives, Source: Greenwich Associates Survey of 118 Institutional Investors in 1998. Further Reading EASY AND ENTERTAINING: ”The Universal Financial Device” Chapter 11 of Capital Ideas by Peter Bernstein. SERIOUS, INTRODUCTORY LEVEL MATERIALS: Options, Futures, and Other Derivative Securities by John Hull. INSTITUTIONAL, FOR PRACTITIONERS: the Risk magazine, published monthly. http://www.riskpublications.com Focus: BKM Chapters 20. • p. 652-657, know how to read listed option quotations, difference American vs. European option • p. 662-670, option strategies • p. 671-673, put-call parity • p. 674-679, know basic information about optionlike securities • p. 683-684, know basic information about exotic options type of potential questions: concept check question 1, 2, 3 & 4, 6, 8, 9, p. 688, question 14 Questions for the Next Class Please read: • BKM Chapters 21, and • think about the following questions: There are two sources of uncertainty affecting the SP 500 index: 1. marginal movements due to small chunks of information arrival. 2. market crashes Neither type is diversifiable, and investors are averse to both. • If we want to gauge the fear of market crash, where do we look? • Why would someone purchase a deep out of the money put option on the SP 500 index?