I kind of expect all three to match but no such luck. Why are SPY and IVV different? Today, 4/27 SPY: Open: 120.65, Close: 118.48 IVV: Open: 121.04, Close: 118.87 It seems that SPY is a bit lower than IVV for some reason. ^GSPC: Open: 1209.92 Close: 1183.71 which doesn't match even after adjusting by 10. I have an inside bar strategy that works on the index data but not on either of the ETFs. Are the futures they way to go?
spy pays dividend, index does not. also the opening price for the index is suspect (not sure what is the reason, maybe because the stocks don't all open at the same time) if your strat is using the open price of the index, may as well throw it away