As us have seen in chapter 2 , fact that we seek supernovæ in extreme cases of detection (what is the case in the case of search for supernovæ with great shift towards the red) can involve the selection of the most brilliant supernovæ and thus bias measurements of cosmology.
However, the supernovæ have weak intrinsic dispersions to the maximum of luminosity, which implies a relatively low bias.
perlmutter1999 & knop2003 showed for research of supernovæ to redshifts of 0.5 that bias was about 0.02 magnitude.
The close supernovæ present the same type of bias even if if in theory research is limited by the depth of the observations. The two effects are thus compensated in good part.