TABLE 4-1 Sample Weights

Race

Male Age Group

Female Age Group

18-29

30-44

45-66

18-29

30-44

45-66

White

1.516531

1.070699

1.473671

1.502991

1.881647

2.407866

African

American

0.835324

0.424599

0.312164

1.000204

0.324416

0.181680

Hispanic

0.808564

0.691170

0.933218

1.124507

1.823606

1.150489

Other

2.332153

1.338566

0.741441

0.597626

0.566132

0.265141

SOURCE: Anthrotech, 2004.

National Laboratory (LANL) face panels (Hack et al., 1974; Hack and McConville, 1978). The proposed face panels are meant to represent the current U.S. workforce, and not the subset of young men and women who belonged to the U.S. Air Force in the early 1970s. However, without additional data comparing the outcome of the LANL face panel and the proposed face panel, including quantitative fit tests, it is not possible for the committee to determine if the updated target population was an improvement and appropriate given the demographics of the current workforce too broad.

Data Stratification

Data stratification is a useful sampling technology that uses information about the reference population to conduct sampling in a more efficient manner. The reference population is broken up into strata based on auxiliary variables (e.g., age, gender, ethnicity, and race), and a random sample of a certain size is obtained from each of the strata. The sample number can be determined based on issues of variability and cost—a problem of optimal design (Neyman, 1934). Typically, and assuming that information about variability within strata is available, the larger the stratum variance, the larger the sample size from that stratum. Stratified sampling works best when strata have small (internal) variability while variability across strata is large by comparison.

In the survey conducted by Anthrotech, the distribution of subjects based on demographics was not known until after the subjects were sampled, thus the sampling plan used a poststratification method. That is, subjects were assigned to the various strata only after they had been sampled and measured. This implies, for example, that the number of



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