Statistical classification methods such as Normix, applied to groups p
reviously formed (a priori groups) using hierarchical methods, ean imp
rove the a priori groups and give estimation of probabilities Far memb
ership. In this study, we used data from the evaluation of 29 maize (Z
ea mays L.) races to (i) apply Normix to the a priori groups formed by
the Ward method (Normix after Ward), (ii) use tile upper tail approac
h and a likelihood ratio test to estimate the optimal number of groups
, and (iii) use three geometrical and statistical criteria (Mahalanobi
s distances, multivariate statistics, and trace and determinant of the
within- and among-group variability matrices) to compare the groups o
btained from Ward per se and the Normix after Ward method. Results ind
icated that the reclassification of accessions by Normix substantially
improved the a priori groups obtained by Ward in four ways: (i) the a
verage Mahalanobis distance between groups was larger among Normix tha
n among Ward groups; (ii) the ratio of variability between groups to v
ariability within groups is increased after Normix compared with that
obtained after Ward; (iii) the generalized variance within groups is d
ecreased in Normix compared with Ward; and (iv) the correlation coeffi
cients between variables are increased after Normix compared with thos
e correlation values obtained by Ward. Results suggested that the grou
ps Foamed by the Normix after Ward procedure allows (i) a good estimat
ion of the optical group numbers, (ii) formation of more compact and s
eparates: groups than the a priori groups formed by Ward per se, and (
iii) estimation of the probability of accession membership to the grou
ps.