Formation rate, ρ(z), of CHIME FRBs and the SFR versus redshift. The thick blue curve and the shaded regions show, respectively, the best fit of SFR = 0.02(1 + z)^2.65/[1 + ((1 + z)/2.95)^4.93] with the theoretical model in Madau & Fragos (2017) and a 2σ confidence level. Grey squares, blue upward triangles, and red circles represent the observed SFR taken from Madau & Dickinson (2014), Thompson et al. (2006) and Hopkins (2004), respectively. The three thick step lines denote the FRB event rates of the three samples. The best fit to sample 3 is displayed by the solid green line.