Slope of the mass-loss rate as a function of metallicity, m, for different values of the luminosity. The top panel shows the empirical determinations of Mokiem et al. (2007), Ramachandran et al. (2019), and Marcolino et al. (2022), along with our determination based on the linear fits as shown in Figs. 4 and 6. The empirical values of m from Rickard et al. (2022) lie above the vertical range of this figure. The bottom panel shows the predicted values of m of Krtička & Kubát (2018) and Björklund et al. (2021), along with our empirical determination. The value of m = 0.83 from Mokiem et al. (2007) is also shown for reference. In all cases, d log v_∞/d log Z = n = 0.13 is assumed (Leitherer et al. 1992).