why the difference series aren't stationary are time series stationary is it a random walk? is the observed difference series stationary when the difference series are stationary what kind of correlation is the dickey-fuller test is the difference series stationary is the observed time series stationary when the difference series are stationary, what happens in the observed time? what does random walk mean is observed data stationary is a time series stationary why a time series is stationary what type of correlation does the observed time series have what is the p value of a difference series are observed time series stationary what type of trend does a time series have is the observed time series stationary? is a time series random or stationary? is the observed time series a random walk? can a time series be described as random