Comparison between the predicted and observed ratios of Eu-free stars over the total number of stars for bins of 0.5 dex in [Fe/H]. Blue and red markers are the observational proxies for the ratio; so the ratio between the number of stars for which Eu only presents an upper limit (possibly Eu-free) over the number of stars with measured Ba. Observational ratios derived from the JINAbase data-set Abohalima & Frebel (2018) are plotted in red. Left panel: ratio of Eu-free stars for model MSFR, M10, M11 (in black), and NSt3 from Cavallo et al. (2021; in orange). Central panel: same as left panel but for models HC0, HC1, and HC2. Right panel: same as left panel but for model MRD0, MRD1 (in black), and HC0 (in green).