Path-level models reveal how sequences influence conversion behavior, while aggregate econometrics estimate contributions when identifiers break or channels lack clicks. Combine them: use MTA for short‑cycle optimization, MMM for budget planning and saturation curves, and cross‑validate with lift experiments. Disagreeing outputs are signals to investigate audiences, creatives, and seasonality, not excuses to cherry‑pick the rosiest number.
Design geo splits, ghost ads, or PSA holdouts to estimate what truly changes when spend moves. Define power, sample size, and primary metrics before launching. Share preregistered hypotheses to deter data dredging, then document learnings publicly across teams so future campaigns reuse insights, shorten cycles, and protect capital from seductive but non‑causal performance illusions.
Broken pixels, inconsistent UTMs, or misconfigured conversions poison ROI faster than bad creative. Standardize naming, enforce governance with automated checks, and monitor anomalies daily. Consolidate events to meaningful outcomes, deduplicate across platforms, and align time zones. When trust improves, debates shift from whose number is right to which decision will most effectively unlock profitable growth.