I use the ADF and KPSS to test for stationarity / non-stationarity of price increments in financial time series.
The two test applied provide different results for low lags, but the same result for higher lags:
Lag = 1: KPSS rejects H(0) is stationary, however ADF rejects H(0) is a unit root in favour for H(1) is stationarity.
Lag = 2: same results as for lag 1.
Lag = 3: both tests indicate stationarity for price increments.
Lag = 4: both tests indicate stationarity for price increments.
Lag = 5: both tests indicate stationarity for price increments.
Are the increments of prices of this financial time seris stationary or not?
The estimation of the generalized Hurst exponent (I use the algorithm provided by Tomaso Aste (2003)) requires that price increments are stationary. What do the results above mean with respect to this requirement?