ReceiptPenny Wise and Pound Foolish: The Left-Digit Effect in Price CognitionManoj Thomas & Vicki Morwitz, Journal of Consumer Research · 2005 · AcademicWhere it bends: Charm pricing works when the left digit changes; it is not a universal lift.Read the source Read the full Crib
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ReceiptThe Unfavorable Economics of Measuring the Returns to AdvertisingRandall A. Lewis & Justin M. Rao, Quarterly Journal of Economics · 2015 · AcademicWhere it bends: This is about measuring marginal ROI precisely, not about whether to experiment: the same paper argues RCTs still inject unbiased information, while targeted advertising makes selection bias crippling for observational attribution.Read the source Read the full Crib
ReceiptThe 95-5 Rule: How advertising worksJohn Dawes, Ehrenberg-Bass Institute / LinkedIn B2B Institute · 2021 · AcademicWhere it bends: The 5% figure is a directional average across categories with long purchase cycles, not a universal constant.Read the source Read the full Crib
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Crib of the day
Myth:A cent is a rounding error.
Evidence:Consumers encode prices left to right, so $2.99 vs $3.00 shifts demand far more than one cent warrants - the left-digit effect, shown across lab and field evidence (Thomas & Morwitz, JCR 2005).
Highest-impact Cribs
Ranked by expected business impact weighted by evidence strength.
The Validity Gap
Measurement
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.
Impact9.4/10
Consensus8.8/10
The Validity Gap
Budget Allocation
Myth:TV's ROI estimates justify current spend levels.
Evidence:Estimating elasticities and ROI across 288 brands, Shapiro, Hitsch & Tuchman find ad elasticities far smaller than the published literature suggests, negative ROI at the margin for more than 80% of brands, and positive overall ROI for only about a third.
Impact9.3/10
Consensus8.2/10
95:5 Rule
Demand
Myth:Your entire B2B budget should chase in-market buyers.
Evidence:At any moment only ~5% of business buyers are in-market; the other 95% are future buyers who must be reached now to be remembered later.
Impact9.5/10
Consensus8.6/10
Attribution
Measurement
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.
Impact9.3/10
Consensus8.4/10
Budget Allocation
Budget
Myth:Performance marketing should get the majority of budget.
Evidence:Across hundreds of IPA case studies, roughly 60% brand / 40% activation maximises long-term profit growth in consumer categories.
Impact9.4/10
Consensus8.6/10
How Advertising Works
Time Horizons
Myth:If ads don't move this week's sales, they didn't work.
Evidence:Across 751 short-term and 402 long-term elasticities from 56 studies (1960-2008), the average short-term advertising elasticity is 0.12 - but the mean long-term elasticity is 0.24, double the short-term, through carryover.
Impact9.2/10
Consensus8.8/10
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