Scientists have been giving especial attention to the estimation of variance components in mixed models in the last decades. Consequently several estimation methods have been proposed, what makes the choice of one among them difficult. Aiming to subsidize users of estimation methods of variance components in unbalanced mixed models, aiming to make a better choice in obtaining these estimatives this paper presents, using numerical examples, the main methods of estimation. It also helps beginners with the introductory concepts they need to use the PROC MIXED programfrom the SAS Statistical system, to obtain the estimatives of variance components trough the available methods there presented, considering the occurence of different matrices of variance and covariance.
PROC MIXED; SAS; variance components; mixed models