Why Modeling Averages Is not Good Enough: A Critique of the Law of Double Jeopardy

For more than 40 years, Andrew Ehrenberg and others have demonstrated the value of the Dirichlet and related distributions as a method for modeling typical brand performance measures (BPMs) in markets.

Why Modeling Averages Is not Good Enough: A Critique of the Law of Double Jeopardy

Martin Bongers and Jan Hofmeyr



According to the law of double jeopardy (DJ) in markets, big brands benefit doubly: They have more users, and their users use them more. More formally: “In all markets, all conventionally used brand performance measures (BPMs) can be predicted from market share using the Dirichlet distribution (once calibrated)” (Chatfield and Goodhardt, 1975).

The law challenges many marketing-research approaches. Consider brand equity. Most attitudinal systems are based on some sort of commitment or engagement ”ladder” (Keller...

Not a subscriber?

Schedule your live demo with our team today

WARC helps you to plan, create and deliver more effective marketing

  • Prove your case and back-up your idea

  • Get expert guidance on strategic challenges

  • Tackle current and emerging marketing themes

We’re long-term subscribers to WARC and it’s a tool we use extensively. We use it to source case studies and best practice for the purposes of internal training, as well as for putting persuasive cases to clients. In compiling a recent case for long-term, sustained investment in brand, we were able to support key marketing principles with numerous case studies sourced from WARC. It helped bring what could have been a relatively dry deck to life with recognisable brand successes from across a broad number of categories. It’s incredibly efficient to have such a wealth of insight in one place.

Insights Team
Bray Leino

You’re in good company

We work with 80% of Forbes' most valuable brands* and 80% of the world's top top-of-the-class agencies.

* Top 10 brands