482
Opinion of O'Connor, J.
placed "may, where he deems it appropriate" with "shall, if he considers it feasible" when it amended § 195 in 1976. Pub. L. 94-521, 90 Stat. 2464. In House of Representatives, we found that this amended language "might reasonably be read as either permissive or prohibitive with regard to the use of sampling for apportionment purposes." 525 U. S., at 339. Even so, we held that § 195 maintained the prohibition on sampling with respect to apportionment given the "broader context" of "over 200 years during which federal statutes [had] prohibited the use of statistical sampling where apportionment [was] concerned." Id., at 339-341. With respect to § 195, then, the only question is whether "hot-deck imputation" is a form of sampling.
To answer this question, I begin with the definition of sampling the Bureau provided to Congress in connection with the year 2000 census:
"In our common experience, 'sampling' occurs whenever the information on a portion of a population is used to infer information on the population as a whole[,] . . . [although] [a]mong professional statisticians, the term 'sample' is reserved for instances when the selection of the smaller population is based on the methodology of their science." Report to Congress—The Plan for Census 2000, p. 23 (revised and reissued Aug. 1997).
Under this definition, the Bureau's use of imputation was a form of sampling. The Bureau used a predefined, deterministic method to select a portion of the population and then used that portion of the population to estimate unknown information about the overall population. The Bureau's imputation process first selected a group of "donor" addresses, one for each address that had not been successfully enumerated. This donor group was a subset of the overall population. Indeed, the donor group was actually a subset of a subset of the population because it was selected from only those addresses that had not returned an initial question-
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