Overview
Budget Shift (BS) is a new metric that quantifies how much spend was reallocated across ads within a budget pool day-over-day, calculated as the total variation distance between consecutive days' spend distributions: 0.5 · Σ|pi − qi|.
A BS of 0.30 means ~30% of the pool's budget effectively moved between ads from one day to the next. Empirically, days exceeding 30% BS show enough reallocation that other performance metrics (CPA, ROAS, BreezeScore) become unreliable signals for that day.
Budget Pool Definition
- CBO: the campaign is the pool
- ABO: the ad set is the pool
Storage and Computation
- BS computed and stored as a percentage (1-100%) per pool per day
- Computed at the pool level (campaign for CBO, ad set for ABO)
- Ad-level and ad set-level (under CBO) charts inherit the BAS of their parent budget pool
Threshold Configuration
- New per-company setting:
bas_threshold, default0.30