as calculated using Eq. (8) as a function of metallicity. The dashed line and shaded area is a linear fit to the data and its 1σ confidence interval respectively, tracing a significant positive correlation between the two variables. The trend is predominantly set by the lowest metallicity points, with those data points at [M/H] > −1 showing no obvious trend. The Milky Way is shown by a black point at [M/H] = 0,  = 1.