This price difference of 30 to 35 was previously unheard of, since
arbitrageurs like us generally kept the two prices within a point or two of each other.
Not exact matches
Like carry trade «
arbitrageurs» who thought parity was suspended just for them, these guys thought risk had become unmoored from return.
Now, to correct this difference, the ETF
arbitrageur (who are these guys anyway, are they big firms
like Goldman) will short some shares of ETF, use the money to purchase the underlying basket of stocks, which will raise the price of underlying stocks, so that now SPY and the underlying mirror each other in price.
There are other risks associated with instruments
like ADR's and cross-listed companies, but normally
arbitrageurs will remove these discontinuities quickly.
Try to think
like an
arbitrageur.