When you turn your TV (or app being it is 2015) to CNBC, Bloomberg, FOX Business, etc. in the mornings you will see numbers for implied opening as it pertains to the indices.
Implied opening is simply the deviation between future value and fair value: Future Value - Fair Value = Implied Opening. The futures market (future value) is open 24/7 and therefore futures will usually not be price aligned with the fair value as fair value represent the trading of the actual (cash index) indices during pre-market. Once the opening bell rings and consequent liquidity picks-up, the indices factor in the futures market and vice versa.
And for the analytic types that does imply there are arbitrage opportunities that institutional investors seek to capitalize upon. However, transactions cost(s) must be taken in to consideration, which reduces or nullifies profits. "As soon as the index futures price premium, or discount to fair value, covers their transaction costs (clearing, settlement, commissions and expected market impact) plus a small profit margin, the computers jump in, either selling index futures and buying the underlying stocks if futures trade at a premium, or the reverse if futures trade at a discount." ( http://www.investopedia.com/articles/active-trading/070113/using-index-futures-predict-future.asp#ixzz3d44JV6Ll )
