On the autocorrelation of the stock market

I introduce an index of market return autocorrelation based on the prices of index options and of forward-start index options and implement it at a six-month horizon. The results suggest that the autocorrelation of the S&P 500 index was close to zero before the subprime crisis but was negative in its aftermath, attaining values around –20% to –30%. I speculate that this may reflect market perceptions about the likely reaction, via quantitative easing, of policymakers to future market moves.