Fraction of galaxies in the MegaZ-LRG sample with high-quality shape measurements, as a function of photometric redshift (top left panel), rest-frame absolute r band magnitude M_r (top right panel), i band de Vaucouleurs magnitude i_deV which was used as a selection criterion for the MegaZ-LRG catalogue (bottom left panel), and apparent observer-frame r band magnitude used to impose a magnitude limit on the shape catalogue (bottom right panel). The red histograms show the match fraction for the full MegaZ-LRG shape sample, and the blue histograms for shape sample with the additional colour cut that will be discussed in Sect. 5.4. For reference we have added to each panel the histogram of the full MegaZ-LRG sample with arbitrary normalisation as black dotted lines. Note that the fraction of galaxies with shape information does not depend strongly on redshift and r band magnitude.