Attribution
The methodology for deciding which marketing touchpoints get credit when a customer converts — first-click, last-click, multi-touch, or model-based.
Attribution answers the question "what made the customer buy?" — and the answer is always partly wrong. Real customers see ten touchpoints across five channels over weeks; attribution models pick one way to split the credit so reporting can move.
For agencies, attribution is the political battlefield of every marketing review. Last-click favours bottom-funnel channels (paid search, retargeting); first-click favours brand and awareness; multi-touch tries to be fair but adds complexity nobody trusts. Pick a model deliberately and document why.
The honest path is to treat attribution as a directional tool, not a verdict. Combine it with incrementality tests (geo holdouts, ad-pause experiments) and media-mix modelling for the bigger budgets. Any agency that promises perfect attribution is either selling something or about to.