“…Indeed, this problem seems not even being mentioned, as can be inferred from important references on the subject, such as Chan and Mak (1985), Fuller (1987), Moon and Gunst (1993), Cheng and Schneeweiss (1998), Schneeweiss and Nittner (2001), Cheng and Schneeweiss (2002), Kuha and Temple (2003), and Kukush et al (2005). A goodness-of-fit test is presented in Cheng and Kukush (2004). The cases focused are the case σ 2 u known (most frequent), the knowledge of the ratio of variances (σ 2 e /σ 2 u ) (Chan and Mak, 1985), and the situation where the covariance matrix in (3) is fully or partially known, with σ eu = cov(e i , u i ) not necessarily null.…”