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Statistical methods can often estimate, to specified levels of accuracy, the characteristics of a “population” or “universe” of events, transactions, attitudes, or opinions by observing those characteristics in a relatively small segment, or sample, of the population.
Acceptable sampling techniques, in lieu of discovery and presentation of voluminous data from the entire population, can save substantial time and expense, and in some cases provide the only practicable means to collect and present relevant data. In one case, for example, a statistical expert profiled the compensatory damage claims of the class members to assist the jury in fixing the amount of punitive damages.
The choice of appropriate sampling methods will depend on the objective. There is a difference between sampling to generate data about a population so the data will be verified or declared true and sampling, like polling, to measure opinions, attitudes, and actions by a population. In the case of the former, the reliability and validity of estimates about the population derived from sampling are critical.
The sampling methods used must conform to generally recognized statistical standards. Relevant factors include whether
Laying the foundation for such evidence will ordinarily involve expert testimony and, along with disclosure of the underlying data and documentation, should be taken up by the court well in advance of trial. Even if the court finds deficiencies in the proponent’s showing, the court may receive the evidence subject to argument going to its weight and probative value.
By contrast, questioning a sample of individuals by opinion polls or surveys about such matters as their observations, actions, attitudes, beliefs, or motivations provides evidence of public perceptions. The four factors listed above are relevant to assessing the admissibility of a survey, but need to be applied in light of the particular purpose for which the survey is offered. In addition, in assessing the validity of a survey, the judge should take into account the following factors:
Parties who propose to offer sampling or survey evidence may want to consider whether to disclose details of the proposed sampling or survey methods to the opposing parties before the work is done (including the specific questions that will be asked, the introductory statements or instructions that will be given, and other controls to be used in the interrogation process). Objections can then be raised promptly and corrective measures taken before the survey is completed. A meeting of the parties’ experts can expedite the resolution of problems affecting admissibility.
Parties sometimes object that an opinion survey, although conducted according to generally accepted statistical methods, involves impermissible hearsay. When the purpose of a survey is to show what people believe—but not the truth of what they believe—the results are not hearsay. In the rare situation where an opinion survey involves inadmissible hearsay, Federal Rule of Evidence 703 nevertheless allows experts to express opinions based on the results of the survey.