Comoving number density (ρ(z)≡dN/dz) as a function of redshift from a simulated distribution of 10⁶ FRBs. The FRBs either follow a constant number density per comoving volume element (Wright 2006), the SFR (Madau & Dickinson 2014), the SMD (Madau & Dickinson 2014), or a power law in the comoving volume space with index α_in = −0.5 or α_in = −2.0 (see Sect. 2.1). Note that dn_FRB refers to the intrinsic number of FRBs and not to an observed number because that would be affected by a factor of (1 + z)⁻¹ as well as the luminosity function, spectral index, etc.