Difference between observed and true metallicity as a function of the true values of metallicity at different redshifts. Top panel: difference between observed and true metallicity as a function of the true values of metallicity at z = 0.30. Each dot is colour-coded according to σ_[Z/H] obtained from the PDF. The green dots are the median values of the [Z/H] differences in bins of Age_r,true, while the error bars are the median of the σ_[Z/H], with each bin having the same number of data points. The cyan dashed line represents the 0 value of the y-axis. Bottom panel: same as the top panel for z = 0.70.