Number density distribution in the 48 ALHAMBRA sub-fields in three magnitude-redshift bins. The mean magnitude and the redshift range of each bin are given in the panels. The total dispersion is shown as a red bar while the star and the black bar mark the median and the intrinsic dispersion retrieved by the MLE, respectively. The red solid lines show the best MLE solutions convolved with the Poisonian errors and are independent of the histogram binning. The derived values of the relative cosmic variance and the corresponding bias values are labelled in the panels.