  The LIGO Scientific Collaboration and the Virgo Collaboration have cataloged
eleven confidently detected gravitational-wave events during the first two
observing runs of the advanced detector era. All eleven events were consistent
with being from well-modeled mergers between compact stellar-mass objects:
black holes or neutron stars. The data around the time of each of these events
have been made publicly available through the gravitational-wave open science
center. The entirety of the gravitational-wave strain data from the first and
second observing runs have also now been made publicly available. There is
considerable interest among the broad scientific community in understanding the
data and methods used in the analyses. In this paper, we provide an overview of
the detector noise properties and the data analysis techniques used to detect
gravitational-wave signals and infer the source properties. We describe some of
the checks that are performed to validate the analyses and results from the
observations of gravitational-wave events. We also address concerns that have
been raised about various properties of LIGO-Virgo detector noise and the
correctness of our analyses as applied to the resulting data.
