Testing the Limits of Expert Testimony Pt. II: Is Your Guess As Good As Mine?

Imagine you contracted to build your dream house.  Then tragedy struck.  The surface bond material holding together the specialized concrete that kept your house in tact was negligently applied.  You sued.  And now you are at trial.  You are assessing who is at fault for the negligent construction.  Who would you prefer to allocate the fault among yourself, the architect, the suppliers, and the subcontractors: (a) a construction expert with sixty-three years of experience who served as the superintendent of an engineering apprenticeship program; or (b) a common jury?  An identical situation was presented in Webb v. Omni Block, Inc., 216 Ariz. 349 (App. 2007).

Ouroriginal ‘Testing the Limits of Expert Testimony’ post discussed the inconsistent application of Arizona Rule of Evidence 704(a), which makes expert opinions that embrace ultimate issues permissible unless the testimony directs, rather than assists, juries.  In Webb, the court applied Rule 704 and held that the expert impermissibly directed the jury by opining on a percentage of fault allocation to be apportioned among the owner, architect, suppliers, and sub-contractors.

The balance Arizona Courts attempt to achieve is to allow expert witness testimony on “issues beyond the common understanding of jurors” without “[directing] juries how to decide cases.”   Porter v. Arizona Dep’t of Corr.  Yet, even though Arizona cases consistently affirm faith in juries to reasonably apportion fault, might fault apportionment be beyond the common understanding of jurors, especially in complex construction disputes involving multiple trades?

In Webb, the jury’s allocation of fault did not match a single recommendation by the expert witness:

  Expert Witness Opined Jury Found
Bistany 25% 27%
Mendoza 30% 0%
Omni 0% 6%
Petrini 10% 22%
ProWall 0% 15%
Webbs 35% 30%

The data prompts several questions.  How did the jury distinguish between a party being 25% and 27% at fault?  On what basis did the jury allocate 15% fault to a party not mentioned by the expert?  Considering the jury’s vast deviation from the expert’s directions, why was the issue of whether the expert witness impermissibly directed the jury not moot?

One reason courts place faith in juries is the strength of unbiased groups.  As psychologist David Johnson discusses in Joining Together: Group Theory and Group Skills, a group of people is more effective at problem solving than a single person by themselves.  In other words, the group of eight to twelve jurors in Webb may have been more accurate in assessing fault than the single expert witness, who was paid by the homeowner and likely worked with an inherent bias in favor of his client.

Still, in an adversarial system where all sides may present expert testimony, what stops the jury from balancing the testimony of multiple experts?   If juries heard expert witness testimony on fault allocation from all sides of a dispute, and juries considered all the testimony together, could the testimony aid, rather than direct, juries?