Correlation between metallicity (12 + log(O/H)) and peak magnitude for the three different metallicity estimators (N2 at the top, O3N2 in the middle, and D16 at the bottom). Each Pearson correlation coefficient ρ is shown along with its standard deviation and p value. The best linear fits are shown with the red lines, and the 1σ region is indicated by the gray shades. No host extinction is applied here.