FINS2624 Lecture Notes - Lecture 11: Arbitrage, Standard Deviation, Log-Normal Distribution
11 – Option Valuation
Pricing Options:
• Options priced using no-arbitrage arguments
• Form portfolio that combines positions in option and its underlying asset, to
replicate risk-free asset
• Options are derivatives whose payoffs depend on the value of the underlying assets
One-Period Binomial Model:
• Setup
Assets:
(a) Underlying asset (e.g. stock) with price S
i Stock can either have high return (price changed by u) or low return
(price changed by factor d)
ii Price of stock at time T, ST, will be either S0u or S0d
(b) Option with premium (i.e. price) f
i Payoff depends on price of stock at time T
ii Payoff either fu (if high return) or fd (if low return)
(c) Risk-free asset paying risk-free rate of rf
Two periods (0 & T)
(a) Want to find arbitrage-free price of option at time 0, f0
Replicating the Risk-Free Asset:
• Payoff in two nodes should be certain (known):
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Pricing options: options priced using no-arbitrage arguments, form portfolio that combines positions in option and its underlying asset, to replicate risk-free asset, options are derivatives whose payoffs depend on the value of the underlying assets. Assets: (a) underlying asset (e. g. stock) with price s i. Two periods (0 & t) (a) want to find arbitrage-free price of option at time 0, f0. Replicating the risk-free asset: payoff in two nodes should be certain (known): Change in option price resulting from a change in stock price. Measures sensitivity of option value to underlying asset price. Cha(cid:374)ge i(cid:374) (cid:448)alue of shorti(cid:374)g optio(cid:374) e(cid:454)a(cid:272)tl(cid:455) offset (cid:271)(cid:455) (cid:272)ha(cid:374)ge i(cid:374) (cid:448)alue of shares of stock portfolio value will not change (i. e. risk free) Also (cid:272)alled (cid:858)hedge ratio(cid:859) of option, value change in one option position (long or short(cid:895) (cid:449)ill (cid:271)e hedged (cid:271)(cid:455) holdi(cid:374)g shares of sto(cid:272)k i(cid:374) opposite dire(cid:272)tio(cid:374: portfolio must earn risk-free rate in absence of arbitrage.