In a recent paper Loveday et al. (1992) have presented new results on the
luminosity function for a sample of galaxies with bJββ€17.15. After having
morphologically classified each galaxy (early--type, late--type, merged or
uncertain), they have estimated the parameters of a Schechter luminosity
function for early-- and late--type galaxies. However, in their sample there is
a bias against identifying early--type galaxies at large distances and/or faint
magnitudes: in fact, many of the early--type galaxies at faint magnitudes have
probably been classified as ``uncertain". As discussed in Loveday et al., the
existence of such a bias is indicated by the fact that for these galaxies
=0.32. In this paper we show, both theoretically and through the
use of simulated samples, that this incompleteness strongly biases the derived
parameters of the luminosity function for early--type galaxies. If no
correction for such incompleteness is applied to the data (as done by Loveday
et al.), one obtains a flatter slope Ξ± and a brighter Mβ with respect
to the real parameters.Comment: accepted for publication on MNRAS, Standard TeX, for tables and
figures contact [email protected] BAP 03-1994-04-IR