Watching your expert witness harassed by an unfair crossexamination, without protection from the trial judge, is one of the most frustrating, annoying, and enraging events in trial. Not so long ago, I had the experience of having a lawyer put a chart together during his crossexamination of an expert witness. The crossexaminer took the upper bound of each confidence interval, and asked “Based upon this study, the true relative risk could be as high as X?” When the witness, naturally and properly pointed out that the study data were also compatible with a relative risk as low as Y, the lower bound of the confidence interval, the crossexaminer whined that the witness was not being responsive, with the trial court’s chiming in to curb the expert’s reasonable desire to have a complete, correct answer.
Watching events such as this crossexamination has led me to believe that there really should be a rule of completeness for statistical evidence. If sampling is random and unbiased, a point estimate may be the best estimate of the true value of a mean or a proportion, but that estimate may be rather crummy if the random error is large. Presenting the sample statistic without some idea of the standard error seems wrong, but is there a remedy?
Statistical evidence did not play much of a role in the development of common law evidence, but the law is concerned with the sort of contextual accuracy that was being abused by the crossexamination of the expert witness, above. The Federal Rules provide for completeness in at least two contexts. Federal Rule of Evidence 106 provides:
“Remainder of or Related Writings or Recorded Statements
If a party introduces all or part of a writing or recorded statement, an adverse party may require the introduction, at that time, of any other part — or any other writing or recorded statement — that in fairness ought to be considered at the same time.”
A similar rule governs depositions presented in court. Federal Rule of Civil Procedure 32(a)(4).
As the Advisory Committee notes to Rule 106 point out, Rule 106 is based upon two basic considerations:
“The first is the misleading impression created by taking matters out of context. The second is the inadequacy of repair work when delayed to a point later in the trial. … The rule does not in any way circumscribe the right of the adversary to develop the matter on cross-examination or as part of his own case.”
Rule 106, Advisory Committee Notes (internal citations omitted).
When “in fairness” should an omitted portion be considered contemporaneously? Here is how the Seventh Circuit put the matter in the more mundane context of a writing:
“To determine whether a disputed portion is necessary, the district court considers whether
(1) it explains the admitted evidence,
(2) places the admitted evidence in context,
(3) avoids misleading the jury, and
(4) insures fair and impartial understanding of the evidence.”
United States v. Velasco, 953 F.2d 1467, 1475 (7th Cir.1992).
Presentation of a point estimate should be accompanied by a measure of its variability; “[w]henever possible, an estimate should be accompanied by its standard error.” Reference Manual on Scientific Evidence at 117-18 (2d ed. 2000). Similarly, trial courts should be vigilant against permitting a party to use the upper or the lower bound of a confidence interval to paint a misleading picture of “what the evidence shows.”
