  The ATLAS detector at the Large Hadron Collider reads out particle collision
data from over 100 million electronic channels at a rate of approximately $100$
kHz, with a recording rate for physics events of approximately 1 kHz. Before
being certified for physics analysis at computer centres worldwide, the data
must be scrutinised to ensure they are clean from any hardware or software
related issues that may compromise their integrity. Prompt identification of
these issues permits fast action to investigate, correct and potentially
prevent future such problems that could render the data unusable. This is
achieved through the monitoring of detector-level quantities and reconstructed
collision event characteristics at key stages of the data processing chain.
This paper presents the monitoring and assessment procedures in place at ATLAS
during 2015-2018 data-taking. Through the continuous improvement of operational
procedures, ATLAS achieved a high data quality efficiency, with 95.6% of the
recorded proton-proton collision data collected at $\sqrt{s}=13$ TeV certified
for physics analysis.
