what is the adf test in financial returns why is the adf test useful in financial returns what is the adf test on volatility is adf test stationary what is stationary in the adf test which of the following data series is stationary how to confirm that a time series is stationary is volatility constant in an adf test dickey fulller test for volatility which model of a time series is stationary what is the alternative hypothesis for adf what is the adf test for financial returns does volatility indicate sp500 is stationary when the volatility of the sample is stationary what adf test indicates volatility of time series is the sp500 series stationary is financial returns time series stationary? which hypothesis shows that a series is stationary how can the adf test conclude that the sp500 series is stationary when a time-series is stationary, why