Panels (a) and (b): deviation of DM_cosmic (ΔDM_cosmic) (pc cm⁻³) from the theoretical curve (solid black line in Fig. 2) as a function of the density increment with WISE × PS1 and SCOS × WISE FRB samples, respectively. The coloring of the data points is the same as Fig. 2. The thin gray lines indicate the individual best-fit linear functions to the data points, randomized with the uncertainties following the Gaussian probability density functions by the Monte Carlo simulations. The solid black line indicates the median of the best-fit linear functions.