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Finance 2 - Lecture 4 summary
Vak: Finance 2 (FEB13001)
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Universiteit: Erasmus Universiteit Rotterdam
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Lecture 4
Properties of stock options and put-call parity
1. If the stock price increases, the probability that spot P > strike P is high, thus buyer of the call
option is better off and is willing to pay more for the option.
The buyer of the put option is worse off and thus, is willing to pay less.
2. If the strike price increases, the probability that strike P > spot P is high, the buyer of the call
option is worse off and is willing to pay less.
The buyer of the put option is better off and thus, is willing to pay more.
3. Because stock P is volatile and both put and call option buyers would like to hedge themselves,
the option prices are higher with increased volatility.
4. When there are dividends, buyer of the call option does not receive them or even in some
instances need to pay them back, he/she is willing to pay less for the option. The reverse is true
for the buyer of the put option.
5. Discount rate is higher, then, the Future P increases, which can be considered as a spot P. As a
result, the probability that spot P > strike P is high, thus, buyer of the call option is better off and
is willing to pay more for the option. The buyer of the put option is worse off and thus, is willing
to pay less.
When the call (put) price is lower than the lower bound for the call price => arbitrage opportunity. The
investment at t=0 is 0, but the profit at time T > 0.
Properties of option prices
Call price cannot be negative; exceed the stock price and be lower than the PV of the difference between
the forward price and the strike price (otherwise, there is an arbitrage opportunity).
Put price cannot be negative; exceed the strike price and be lower than the PV of the difference between
the strike price and the forward price.
Put-call parity
Synthetic forward (buy the call and sell the put) must be priced consistently with actual forwards. Put-
call parity is a principle that defines the relationship between the price of European put options and
European call options of the same class, that is, with the same underlying asset, strike price and
expiration date. Put-call parity states that simultaneously holding a short European put and long
European call of the same class will deliver the same return as holding one forward contract on the same
underlying asset, with the same expiration and a forward price equal to the option's strike price. If the
prices of the put and call options diverge so that this relationship does not hold,
an arbitrage opportunity exists, meaning that sophisticated traders can earn a theoretically risk-free
profit.