Quote from Rob on Business:
Thanks, CMNS2, I will look up those books. I've never heard anyone yet say that being right about underlying and wrong about understanding on other related issues can work against you, yet it must be true judging by how much space you guys devote to talking about it. Those are things never talked about in the introductory seminars I attended and read. I know about expiry and time decay of course, but how much influence volatility has is invisible to me.
Implied volatility (IV) is a coefficient used in the Black-Scholes option pricing model / formula. Simply put: when IV is high options are more expensive, when it is low they're cheaper. Many people confuse it with historical volatility (standard deviation of the past stock prices) and future implied volatility (the IV estimated value at a given moment in the future). Given all the inputs of the B-S model (stock price, time to expiration, interest rate, dividend, strike) and the option price, the option IV can be calculated, and used to compare different options between them, and also to compare to the historical range of the IV for that stock.
Again, simply put: if the current IV is high relative to the IV historical values, the options may be overpriced, and people may expect the IV to drop (to revert to the mean). This would suggest to sell options now then buy them back after the IV drops (buy low and sell high). In reality you can't be sure what and when'll happen with the IV, you just make an "educated guess" based on whatever methods you like (technical analysis, star gazing, fundamental research, etc.).
Many option quote sites give you besides the option price it's current IV (derived from the B-S formula).
How can you lose money when the stock moves your way? Let's say you buy a call. The stock price goes up, but it's IV goes substantially down: this may cause your call to lose value. Possible scenario: GOOG earnings approach, you estimate a good report and buy calls, but because people are nervous about the news they buy avidly puts and / or calls pushing the IV higher. The news come out, they're good as you predicted, GOOG price goes up, but now people start to relax, they're not rushing to buy puts and / or calls, so IV drops. Depending on how much the stock price went up and how much IV went down, you may have actually lost a lot of money although you were correct. In this scenario, if you took the other side of the trade (you sold the call) you could actually make money although you were wrong about GOOG price.
This is why when trading options you have to predict not only the underlying price direction over your option time frame, but the option future IV relative to its current IV.
You can find a crush introduction in volatility in the following post:
http://finance.groups.yahoo.com/group/OptionClub/message/5344