Attribution window

An attribution window, also called a lookback window, is the period after an ad view or click during which a purchase or other conversion can be credited to that ad.

The window decides how much a report claims. Longer windows credit more sales, including many that would have happened anyway. The IAB/MRC Retail Media Measurement Guidelines of January 2024 set the rules for retailers. Windows must be supported by evidence, fit the campaign's goals and the category's purchase cycle, and stay consistent across similar objectives. They must be disclosed before the campaign runs and again with the results (IAB/MRC Retail Media Measurement Guidelines, January 2024, page 27).

The guidelines do not prescribe a length. They note that digital windows are often 3, 7, 14, 28 or 30 days, and they encourage day-level data so users can reconcile reports that use different windows. Where a retailer projects a campaign's full 12-month effect from a short window, it must disclose the basis. Click windows and view windows are usually set separately, and view windows deserve more scepticism.

Example: A brand compares two retailers. One reports $55,000 in sales on a 14-day window, the other $40,000 on a 7-day window. Using day-level data, the brand recalculates both at 7 days and finds the first retailer drove $36,000, so the second performed better.

Related terms: closed-loop measurement, ROAS, iROAS, incrementality, MTA, new-to-brand.

Authoritative source: IAB and MRC, "Retail Media Measurement Guidelines" (January 2024), section "Attribution windows".

Read the full guide: Retail media measurement standards explained.