Lengthen your attribution window: Which digital ads have most long-term impact?

Brands usually invest in a portfolio of digital ad products for brand consideration and conversion, and their performance is commonly evaluated with ad-attributed metrics. However, these metrics limit the measurement of advertising effectiveness within a short time window, typically of two weeks. Therefore, they could underestimate the total effect if some ad products' efficacy lasts beyond the measurement period. In particular, this could understate the impact from ad products aimed at awareness and consideration. In addition, this bias could manifest in product categories where shoppers' involvement is high because they are making deliberate purchase decisions. To solve these problems, the Vector Autoregressive Moving Average with Exogenous variables (VARMAX) model is applied, which allows flexibility in the length of the advertising measurement window, and thus can empirically quantify how long the effect of each ad lasts without `a priori` restrictions. For 15 US brands across three verticals (Hardlines, Softlines and Consumables) on Amazon, it was found that within the two-week attribution window, upper/middle-funnel ad products only materialise 30–50 per cent of the total effects, compared to lower-funnel at 60–90 per cent. Based on these results, it is recommended that advertisers and publishers lengthen the attribution window, and especially track their upper and middle-funnel ad products for at least a month to capture their longer-term effects.