Purity as a function of redshift for groups identified in a spectroscopic catalogue using an LF varying with redshift and V₀ = 130(1 + z) km s^-1 to compute the linking length parameters. Left panels correspond to low-membership groups while right panels are the high membership ones. The top panels show the fraction of galaxies identified that can be associated with galaxies of the group with the highest matching rate in the corresponding control sample (solid lines), and the fraction of galaxies that are classified as interlopers (dashed lines). The bottom panels show the trends observed for the fraction of groups within the six categories of purity (see text for description). The key for colours and line types is the same as in the previous figure.