Stationarity Stationarity is a fundamental property underlying almost all time series statistical models a time series yt is said to be stationary if it satisfies the following conditions ( 1)E(=u, for all t (2)Var(y)=elo-u=o+ for all t ()Cov(y,, yi-k)=rk for all t8 Stationarity  “Stationarity” is a fundamental property underlying almost all time series statistical models.  A time series yt is said to be stationary if it satisfies the following conditions: 2 2 (1) ( ) . (2) ( ) [( ) ] . (3) ( , ) . t y t t y y t t k k E y u for all t Var y E y u for all t Cov y y for all t   − = = − = =