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Overlapping Shopper (Cross Shop) Views

What Is It?

The Cross-Shopper Model, or “By Overlap” view, quantifies how much overlap exists between the customer bases of two brands.

“Do people who shop at Brand A also shop at Brand B?”

This model assigns a score from -1 to +1 representing the statistical affinity between two brands. It enables analysts to uncover shared audiences, competitor adjacency, and potential co-marketing opportunities.


Why It Matters

Understanding customer overlap unlocks insights for:

  • Competitive Benchmarking — identify direct and indirect rivals based on audience overlap
  • Co-Marketing Strategy — find potential partners that share loyal customers
  • Churn Analysis — detect where customers are drifting
  • Audience Expansion — identify adjacent brands your customers already trust

How It Works

Carbon Arc’s Cross-Shopper Model uses Normalized Pointwise Mutual Information (nPMI) to evaluate brand-to-brand customer overlap each month.

Affinity Score Breakdown

Affinity ScoreMeaning
+1Perfect overlap — identical customer sets
> 0Statistically significant positive overlap (shared audience)
0No measurable affinity
< 0Shared customers less than expected by chance (anti-affinity)
-1No overlap at all

Even if two brands share customers, a negative score may result if that overlap isn’t statistically significant.


Example Use Cases

Use CaseValue
Competitive AnalysisDetermine core vs. fringe competitors by overlap strength
Brand PartnershipsCo-market with brands sharing your top user segments
Customer RetentionSpot potential churn to overlapping competitors
Product StrategyUnderstand which adjacent categories your shoppers engage with

Model Logic

The model computes overlap monthly using:

  • Unique customer counts for each brand
  • Total customers in the ecosystem that month
  • Count of customers shared between both brands

The result is normalized using PMI to account for brand size and total universe.


Output Format

Brand ABrand BMonthAffinity Score
NikeAdidas2024-030.45
SephoraUlta2024-030.83
CostcoWhole Foods2024-03-0.21
  • Only includes brand pairs with ≥10 users per brand per month
  • Optionally excludes brand pairs with zero overlap (score = -1)

Key Metrics

  • Shared Customers: Unique users transacting with both Brand A and Brand B in a given month
  • nPMI Score: Normalized Pointwise Mutual Information score between -1 and +1

Availability

  • Delivered monthly as brand-to-brand affinity tables
  • Integrated into dashboards, brand trackers, and LTV measurement pipelines