Literature compilation of the chemical abundance pattern of Ca as a function of [Fe/H]. Symbols show GCs in the MW from Pritzl et al. (2005; blue) and M31 (green) from Colucci et al. (2014) and Sakari et al. (2015). The pattern of MW disc and halo stars are shown as a logarithmically-scaled number density distribution of arbitrary units (data from Venn et al. 2004 and Roederer et al. 2014). Outliers with significantly lower [Ca/Fe] are highlighted with large open black circles.