Panels (a) and (b): Macquart relation, i.e., DM_cosmic (pc cm⁻³) as a function of redshift, with the WISE × PS1 and SCOS × WISE FRB samples, respectively. The high-density (δ>0) FRB samples are denoted as red data points, and the low-density (δ≤0) FRB samples are represented by blue data points (see Section 2.3 for the details of the galaxy number-density calculation). The FRB samples with upper limits on τ are marked with open circles on the data points. The solid black line shows the theoretical prediction of the average DM_cosmic, 〈DM_cosmic〉, as a function of z by adopting the Planck18 cosmology (Planck Collaboration VI 2020) and the fraction of the cosmic baryons in the diffuse gas, f_d = 0.85. The gray shaded region shows the expected scatter of DM_cosmic due to the cosmic variance (McQuinn 2013; Cordes et al. 2022).