The blue number counts disagree strongly with predictions based on simple models of galaxy evolution. These models can, however, reproduce the infrared number counts reasonably well. No satisfactory explanation of this paradox has been put forward. One of the main difficulties with the interpretation of the observations is the proper modeling of the selection effects and biases in the observations of distant galaxies.
Most models begin with a simplified representation of galaxies in the nearby universe.
Typically, galaxies at low redshift are divided into a few morphological classes, each characterized by a luminosity function and single color. The star formation timescale in each class is then fixed to reproduce this color. These simplistic models may fail to adequately represent the galaxy population at low redshift, and may therefore be an important component in our inability to understand the distant field galaxy observations. A paper by Koo et al. After a successful model of the distant galaxies is found, they compare the predicted luminosity function of the local universe to the available observations.