Cite as: 536 U. S. 304 (2002)
Rehnquist, C. J., dissenting
Errors and Survey Costs (1989); 1 C. Turner & E. Martin, Surveying Subjective Phenomena (1984).
The Federal Judicial Center's Reference Manual on Scientific Evidence 221-271 (1994) and its Manual for Complex Litigation § 21.493, pp. 101-103 (3d ed. 1995), offer helpful suggestions to judges called upon to assess the weight and admissibility of survey evidence on a factual issue before a court. Looking at the polling data (reproduced in the Appendix to this opinion) in light of these factors, one cannot help but observe how unlikely it is that the data could support a valid inference about the question presented by this case. For example, the questions reported to have been asked in the various polls do not appear designed to gauge whether the respondents might find the death penalty an acceptable punishment for mentally retarded offenders in rare cases. Most are categorical (e. g., "Do you think that persons convicted of murder who are mentally retarded should or should not receive the death penalty?"), and, as such, would not elicit whether the respondent might agree or disagree that all mentally retarded people by definition can never act with the level of culpability associated with the death penalty, regardless of the severity of their impairment or the individual circumstances of their crime. Second, none of the 27 polls cited disclose the targeted survey population or the sampling techniques used by those who conducted the research. Thus, even if one accepts that the survey instruments were adequately designed to address a relevant question, it is impossible to know whether the sample was representative enough or the methodology sufficiently sound to tell us anything about the opinions of the citizens of a particular State or the American public at large. Finally, the information provided to us does not indicate why a particular survey was conducted or, in a few cases, by whom, factors which also can bear on the objectivity of the results. In order to be credited here, such surveys should be offered as
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