“…To further investigate the robustness of our findings, various other X-matrix specifications were tried, including (i) use of boolean (dummy) vectors, as would be used, for example, when working with models with outliers or structural breaks, and (ii) the matrix E k , specified as the first k eigenvectors of the first order difference matrix, for various values of k. Matrix E k is given by x it = cos[(2t − 1)π(i − 1)/(2T )] (see Durbin and Watson, 1971), and is a useful benchmark because these vectors tend to mimic the behavior of economic time series with seasonal and cyclical-type behavior (Dubbelman, Louter and Abrahamse, 1978;King, 1985, p. 32). For all X-matrices considered, the ranges for which the respective estimators perform best were virtually identical.…”