Top panel: Fraction of the selected RS galaxies over the total (λ_RS/λ) in each group, as a function of redshift for the sample with identified RS. The yellow and blue lines indicate the mean fraction in each z-bin weighted by the group S/N (size of red points is proportional to the group S/N), using matched observed and rest-frame colors for the fit, respectively. Bottom panel: Fraction of groups with identified RS at different S/N (or purity) levels, as a function of redshift, showing the first consistent appearance of RS in groups at z ∼ 2 − 2.5.