Behavior Change Tracking is the longitudinal measurement capability that proves Catalyst's guidance works. Rather than measuring a single interaction, it tracks traveler behavior over time to identify real shifts: Is this traveler booking further in advance than they were three months ago? Has their preferred supplier adoption rate improved? Are they consistently staying closer to rate targets? The system maintains behavioral baselines per traveler and per cohort, then measures deviation from those baselines after Catalyst guidance is deployed. This is the evidence layer that separates Catalyst from tools that can only report on content delivery.