A defensible reallocation starts neither from average ROAS ranking nor one bad week.
A defensible reallocation starts neither from average ROAS ranking nor one bad week. It requires a persistent signal, a genuinely movable slice, a destination still within its documented range and a prudent gain above transition costs. The rule states trigger, cap, safeguards, review date and return condition.
Decision and method.
Authorise a transfer only if expected prudent gain remains positive after cost and source-channel minimums are protected. Qualify a trigger aligned to the decision—marginal contribution, incremental cost, saturation, capacity or availability—with minimum period, reference and uncertainty. Compare contribution lost at source with contribution expected at destination; retain a prudent bound, subtract transition costs and continuity minima. Test coverage, learning volume, stock, service, calendar and correlations: a blocking constraint prohibits the move even when central gain is positive. Log amount, hypotheses, owner, effective date, observation window and conditions to continue, stop or restore. Define review date, stop signal and restoration reserve before execution.
Worked example.
In an illustrative case, channel A has prudent marginal return 0.10, channel B 0.62. A has €500,000 but must retain a €420,000 floor; transition cost is €6,000. Maximum movable slice: 500,000 − 420,000 = €80,000. Gross prudent gain: 80,000 × (0.62 − 0.10) = €41,600. After transition: €35,600. The rule authorises €40,000 immediately then €40,000 after review. It blocks any further transfer until B response and A coverage are re-estimated.
Checks and limits.
Use a horizon-appropriate incremental or marginal trigger; respect minima, maxima, commitments and observed ranges; require positive prudent gain after transition cost; write review date, stop threshold and return condition before execution. A rule cannot repair biased measurement or badly identified response curves; channel interactions can invalidate separately estimated effects; brand effects and long lags may require dedicated floors; changes too frequent disrupt learning and evaluation.
Resources and sources.
Download the reallocation register. Related: marginal return, response curves, formalise constraints, review a reallocation case. Sources: Google Meridian ROI/mROI and response curves (2026); Google Meridian visualisations (2026); Meta Robyn MMM analyst guide.