There are numerous subtle and less-subtle biases in distance measurement; see [213] for a blow-by-blow account. The
simplest bias, the “classical” Malmquist bias, arises because, in any population of objects with a distribution in intrinsic
luminosity, only the brighter members of the population will be seen at large distances. The result is that the inferred average
luminosity is greater than the true luminosity, biasing distance measurements towards the systematically short. The Behr
bias [12*] from 1951 is a distance-dependent version of the Malmquist bias, namely that at higher distances, increasingly bright
galaxies will be missing from samples. This leads to an overestimate of the average brightness of the standard candle which
becomes worse at higher distance.