“…First, the technically correct parameters to estimate are the conditional variances and covariances, which take account of possible systematic changes in the mean, at least of the spot prices (Myers & Thompson, 1989). Second, since the conditional variances and covariances likely are not constants, empirical estimates should allow for this possibility (for an example and related references, see McNew & Fackler, 1994). Nonetheless, such time-varying covariance estimation is costly and often does not result in greater hedging effectiveness relative to unconditional hedge ratios (Garcia, Roh, & Leuthold 1995;Myers, 1991).…”