Incrementality
Myth:Bidding on your own brand name is always wasted money.
Evidence:Bing field experiments across thousands of brands show brand ads add a small but real 1-4% click lift when no competitor bids, and become defensive when rivals bid to siphon the traffic.
Pairs with the eBay result: pause when uncontested, defend when contested. The right answer is auction-specific, not ideological.
Andrey Simonov, Chris Nosko & Justin M. Rao, Marketing Science · 2018 · Academic
Channels: paid · search · measurement
Incrementality
Myth:Platform-reported ROAS is sufficient evidence.
Evidence:Geo-based holdout experiments give unbiased incrementality estimates without user-level tracking and are the most practical causal method for most advertisers.
Incrementality
Myth:Your ad spend only builds demand for you.
Evidence:Randomized field experiments on a restaurant-search platform show ads also lift sales for non-advertised competitors; spillovers concentrate on same-cuisine, highly rated rivals and are largest when ad intensity is low.
Incrementality
Myth:TV is unmeasurable brand-building with no short-term effect to capture.
Evidence:In two-minute windows around 1,224 commercials across 20 brands and $3.4B in spend, TV ads produce immediate, measurable lifts in site traffic and transactions.
The Validity Gap
Myth:A big enough A/B test or attribution platform can pin down each campaign's ROI.
Evidence:Across 25 large field experiments with major U.S. retailers and brokerages, the median confidence interval on ad ROI was over 100 percentage points wide; individual-level sales are so volatile (coefficient of variation ~10) that an informative test often needs 10M+ person-weeks.
Attribution
Myth:Last-click attribution is a fair scorecard.
Evidence:Large-scale field experiments show branded search and retargeting capture credit for conversions that would have happened anyway; last-click can overstate paid value by an order of magnitude.
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