Last-click / first-touch attribution
Two all-or-nothing rules: give a conversion entirely to the final touchpoint, or entirely to the one that started the journey.
See it
What it is
Last-click attribution gives 100% of a conversion to the final eligible touchpoint before it. First-touch attribution gives 100% to the initial eligible touchpoint instead. One flatters the channel that closed the journey; the other flatters the channel that introduced it.
Reach for either when you need a simple, auditable rule and accept that it throws the rest of the path away. First touch is useful for asking what started discovery. Last click is useful for asking what immediately preceded the outcome. Showing both side by side often reveals how strongly the chosen rule changes the story.
Gotcha: 'first' and 'last' are incomplete definitions. First ever or first inside the attribution window? Last click or last view? Does a direct visit replace a known campaign, or does the rule skip it, which is the variant called last non-direct click that Universal Analytics made the industry default for a decade? Write those choices beside the report, or two correct implementations can disagree while sharing the same label.
Ask AI for it
Write a BigQuery query that computes first-touch and last-click attribution side by side. Join touchpoints to conversions by user_id, keep only touches at or before converted_at and within a 30-day window, then use ROW_NUMBER ordered ascending for first touch and descending for last click. Exclude impressions from the last-click model, keep direct as an explicit channel, and return conversion count and revenue by channel for both models. Add tests for tied timestamps, no eligible touch, and multiple conversions by one user.