Metallicity dependence on the linear SFR scaling relation of HMXB luminosity. Oxygen fractions are derived from mass-weighted stellar metallicities of SSPs younger than 30 Myr. The black solid line is the mean global model calculated by L21 in the limit of perfect luminosity function sampling. The shaded gray area is its 16^th-84^th percentile margin. Our data are binned by oxygen fraction and SFR; SFR bins are indicated by color. Vertical error bars correspond to the 25^th–75^th percentile margin of the data within each metallicity bin, and horizontal black bars indicate the width of the metallicity bin. Colored symbols corresponding to the SFR bins are displaced horizontally with respect to the metallicity bin center for illustrative purposes. The dashed purple line is the corresponding M12b model where no explicit metallicity dependence is assumed.