  It is usual, in gamma-ray burst (GRB) studies, to compare the average
properties of bright and faint GRBs, with the assumption that brightness
classes reflect distance classes. When brightness is intented to reflect the
distance to the sources, it is nevertheless important to use a quantity with a
small intrinsic dispersion. We propose here a method to compare the intrinsic
dispersion of various measures of GRB brightness. This method assumes that
nearby bursters are homogeneously distributed in an Euclidean space with no
density or luminosity evolution. We then use it to compare 5 measures of GRB
brightness in the BATSE Catalog. Our analysis reveals that better (i.e. less
dispersed) measures of brightness are obtained at low energy and that GRBs are
much closer to standard candles below 100 keV than above. We suggest that a
beaming of the emission above 100 keV could explain this behaviour.
