Lag of a time series
= Lag of a time series
{title2=$h$}
A <lag of a time series> is a separation between observation indices. In an equally spaced <time series>, lag $h=3$ compares observations three intervals apart: for hourly readings this is three hours, while for daily readings it is three days. Positive and negative lags describe the same separation in opposite directions. The <autocovariance> and <autocorrelation> of a real <weakly stationary process> are even functions of lag.