“…Y i À f h t i 2 can be utilized in principle to detect deviations from U k in any non-parametric direction, see Schmidt (1979), Bunke & Schmidt (1980), Zwanzig (1980), Bunke (1981), White (1980White ( , 1981, Benzekri & Brodeau (1991). Tests which are directly based on the LSE, however, require knowledge of the variance r 2 t of et or of the ÔÔbest ®tting'' parameter random design assumption (Dette & Munk, 1998b) in the case of linear regression models.…”