Recent empirical studies suggest that many observed financial time series have a slowly declining correlogram or, equivalently, have an infinite spectrum at zero frequency.

• 近来的实证研究发现许多观察到的金融时间序列具有缓慢减少的相关系数或者等价地在0频率下具有无限频谱，这种性质被称为长期记忆性。