I was analysing ibex implied volatility and when I draw it I found it was reversed:
X axis are the strikes and Y axis implied volatilities calculated by BS. The blue line is the spot price. Data (option price and strike) is gotten from MEFF daily info (http://www.meff.com/docs/Ficheros/boletin/esp/boletinpfri.htm).
I first thought I made a mistake but I checked with SP500 and I obtained a normal smile volatility.
Do you have any idea why it has this shape? Hull says that it’s possible when a single large jump is anticipated but he talks about a stock not an index.
Thanks a lot