Context matters more than statistics. A 10% drop on a Monday after a bank holiday is normal. The same drop on a Wednesday is worth investigating. Always check for obvious explanations before escalating.
Strong answers describe a process: establishing baselines, understanding expected variation, using statistical methods (z-scores, IQR, moving averages) or simple rules, and investigating anomalies before raising alarms. Best candidates discuss both false positives (crying wolf) and false negatives (missing real issues), and how they calibrated their detection thresholds.
Tests analytical judgment. Analysts who flag every fluctuation lose credibility. Those who miss genuine anomalies miss their core responsibility. Look for calibrated judgment and a systematic investigation process.