On Being an Ethical Statistical Expert in a Legal Case

Abstract

In the Anglo-American legal system, courts rely heavily on experts who perform an essential social function in supplying information to resolve disputes. Experts are the vehicles through which facts of any technical complexity are brought out. The adversarial nature of this legal system places expert witnesses in a quandary. Enjoined to serve the court and their profession with unbiased, independent opinion, expert witnesses nevertheless do not work directly for the court: they are employed by advocates (lawyers) who aim to win a high stakes debate for their clients. The system is imperfect. Pressures (whether real or perceived) on experts to please their clients may cause truth to be the victim. We use examples from our experience, and reports of statisticians commenting on theirs, to show how statistical evidence can be honestly and effectively used in courts. We maintain it is vital for would-be experts to study the rules of the legal process and their role within it. (The present article is a step toward that end.) We explain what the legal process looks for in an expert and present some ways in which an expert can maintain their independence and avoid being co-opted by the lawyer who sponsors them. Statisticians contribute in sometimes unique ways to the resolution of disputes, including in forums like negotiations, mediation, arbitration, and regulatory hearing, where the misuse and abuse of statistical procedures occur too often. It is a challenge for statisticians to improve that situation, but they can find professional opportunities and satisfaction in doing so. Because this discussion pertains generally to the application and communication of statistical thinking, statisticians in any sphere of application should find it useful.

keyword:

• Ethics
• Expert witness
• Law
• Statistical consulting

Acknowledgments

Comments by referees, the associate editor, and George Cobb led to substantial improvements in the article. Thanks also to Michael Finkelstein, Richard Goldstein, Jay Kadane, David Kaye, Ji-Hyun Lee, and Sandy Zabell for very helpful comments and Ron Wasserstein for ongoing encouragement.