Upper: distribution of the ΔM/M ratio, where ΔM is the average 1σ error bar for each object, at z ~ 2 (left) and z ~ 3 (right). Black solid histograms refer to the GOODS-ERS sample, whereas red dotted ones represent the GOODS-MUSIC data set. Lower: median ΔM/M in each of the redshift bins used in this work as a function of the central redshift for GOODS-ERS (black solid circles/solid lines) and GOODS-MUSIC (red open boxes/dotted lines).