Robust standard error for a time series mean.
Hello. I have a non-stationary time series of returns and I would like to calculate the standard error for the mean of that series. When I use the White-estimator or assume constant variance I got the same results. When I use the Newey-West-estimator, which also cares about autocorrelation, the standard errors increase a lot. 1. What is the right estimator? 2. Is the Newey West estimator strongly affected by the non-stationarity? Does anyone have any literature source or a link to a paper or something like that? I hope someone can help me. Thank you in advance. Sincerely, Andy.