Metallicity distributions predicted by models M1 (left panel), M2 (middle panel), and M3 (right panel) with the best-fit model parameters (colored histograms). The observed APOKASC distribution calculated including both high-α and low-α stars is shown by the black empty histograms. The solid lines indicate the metallicity distribution of our chemical evolution models convolved with a Gaussian with standard deviation σ = 0.118 dex (average APOKASC data error). In each plot the distributions are normalised to the corresponding maximum number of stars N_max.