Relative statistical 1 σ error on the L₅₀₀ luminosity. Input catalogues for each cluster are identified by different symbols and colours, as labelled in the figure. WARPS clusters are not shown since no uncertainties were published in the source catalogue. Left scatter plot of the relative uncertainty as a function of redshift. Right: Corresponding distribution of uncertainties for each input catalogue. The MACS catalogue includes a significant number of systems for which the luminosities come from Chandra follow-up observations, hence the smaller statistical uncertainties.