  Gamma-ray bursts (GRBs) are ultra-relativistic collimated outflows, which
emit synchrotron radiation throughout the entire electromagnetic spectrum when
they interact with their environment. This afterglow emission enables us to
probe the dynamics of relativistic blast waves, the microphysics of shock
acceleration, and environments of GRBs. We perform Bayesian inference on a
sample of GRB afterglow data sets consisting of 22 long GRBs and 4 short GRBs,
using the afterglow model "scalefit", which is based on 2D relativistic
hydrodynamic simulations. We make use of Gaussian processes to account for
systematic deviations in the data sets, which allows us to obtain robust
estimates for the model parameters. We present the inferred parameters for the
sample of GRBs, and make comparisons between short GRBs and long GRBs in
constant-density and stellar-wind-like environments. We find that in almost all
respects such as energy and opening angle, short and long GRBs are
statistically the same. Short GRBs however have a markedly lower prompt
$\gamma$-ray emission efficiency than long GRBs. We also find that for long
GRBs in ISM-like ambient media there is a significant anti-correlation between
the fraction of thermal energy in the magnetic fields, $\epsilon_B$, and the
beaming corrected kinetic energy. Furthermore, we find no evidence that the
mass-loss rates of the progenitor stars are lower than those of typical
Wolf-Rayet stars.
