Hello, I've been investing in the S&P 500 etfs. I know they track the underlying assets closely. In fact, during the day, if the S&P goes up by 0.3%, the etf will do essentially the exact same thing, almost instantaneously. That makes me very comfortable . I am interested in some sector etfs like those from iShares, PowerShares, and SPDR. I want those to do the same thing: the price of the etf should move along with the value of the underlying assets. For example, suppose the sector etf has only two stocks in it, equally weighted. One stock goes up 0.6% and the other goes up 0.8%. I would want the etf to go up 0.7%. Do the iShares, PowerShares, and SPDR industry/sector etfs track along with their underlying assets the same way the S&P etfs do? I would love for that to be the case. If the price of sector etfs have minds of their own (i.e. the price is not simply a function of the value of the underlying assets), that would get me concerned. It could create a bubble, where you would overpay for the fractional interest of the stocks you are getting. I'm currently interested in ITA, the iShares aerospace & defense. I'm hoping it tracks its stock bundle accurately, the way the IVV tracks the S&P bundle accurately.