  We use mock galaxy survey simulations designed to resemble the Dark Energy
Survey Year 1 (DES Y1) data to validate and inform cosmological parameter
estimation. When similar analysis tools are applied to both simulations and
real survey data, they provide powerful validation tests of the DES Y1
cosmological analyses presented in companion papers. We use two suites of
galaxy simulations produced using different methods, which therefore provide
independent tests of our cosmological parameter inference. The cosmological
analysis we aim to validate is presented in DES Collaboration et al. (2017) and
uses angular two-point correlation functions of galaxy number counts and weak
lensing shear, as well as their cross-correlation, in multiple redshift bins.
While our constraints depend on the specific set of simulated realisations
available, for both suites of simulations we find that the input cosmology is
consistent with the combined constraints from multiple simulated DES Y1
realizations in the $\Omega_m-\sigma_8$ plane. For one of the suites, we are
able to show with high confidence that any biases in the inferred
$S_8=\sigma_8(\Omega_m/0.3)^{0.5}$ and $\Omega_m$ are smaller than the DES Y1
$1-\sigma$ uncertainties. For the other suite, for which we have fewer
realizations, we are unable to be this conclusive; we infer a roughly 70%
probability that systematic biases in the recovered $\Omega_m$ and $S_8$ are
sub-dominant to the DES Y1 uncertainty. As cosmological analyses of this kind
become increasingly more precise, validation of parameter inference using
survey simulations will be essential to demonstrate robustness.
