  We compare the dispersion measure (DM) statistics of FRBs detected by the
ASKAP and Parkes radio telescopes. We jointly model their DM distributions,
exploiting the fact that the telescopes have different survey fluence limits
but likely sample the same underlying population. After accounting for the
effects of instrumental temporal and spectral resolution of each sample, we
find that a fit between the modelled and observed DM distribution, using
identical population parameters, provides a good fit to both distributions.
Assuming a one-to-one mapping between DM and redshift for an homogeneous
intergalactic medium (IGM), we determine the best-fit parameters of the
population spectral index, $\hat{\alpha}$, and the power-law index of the burst
energy distribution, $\hat{\gamma}$, for different redshift evolutionary
models. Whilst the overall best-fit model yields
$\hat{\alpha}=2.2_{-1.0}^{+0.7}$ and $\hat{\gamma}=2.0_{-0.1}^{+0.3}$, for a
strong redshift evolutionary model, when we admit the further constraint of
$\alpha=1.5$ we favour the best fit $\hat{\gamma}=1.5 \pm 0.2$ and the case of
no redshift evolution. Moreover, we find no evidence that the FRB population
evolves faster than linearly with respect to the star formation rate over the
DM (redshift) range for the sampled population.
