TABLE 3-1 Proposed Demographic Sample Distribution

Race

Male Age Group

Female Age Group

18-29

30-44

45-65

Total

18-29

30-44

45-65

Total

White

166

166

166

498

166

166

166

498

African

166

166

166

498

166

166

166

498

American

Hispanic

166

166

166

498

166

166

166

498

Other

166

166

166

498

166

166

166

498

Total

664

664

664

1,992

664

664

664

1,992

SOURCE: Anthrotech, 2004.

NIOSH requested that Anthrotech obtain measurements from 166 subjects in each age, gender, and racial/ethnic category. The proposed number of 166 subjects per category was based on a standard developed by the International Organization for Standardization (ISO). Standard 15535 recommends n = (1.96 × CV/a)2 × 1.534, where n is the sample size per cell, CV is the coefficient of variation for a specific measurement (standard deviation divided by mean times 100), and a is the level of precision desired. The investigators chose to define CV based on the menton-sellion length (CV=6.5/121.9=5.3%), as it was one of the more biologically variable measurements. Thus, if the CV is met for this measurement, it would likely also be met for the other measurements (Zhuang, 2001). The 95 percent confidence limits (reflected in the term 1.96), the choice of a 1 percent level of precision (1 percent of the mean), and the value 1.534 (a constant computed using a Bonferroni type of argument to adjust for the multiple comparison) were based on procedures outlined in the ISO 15535—General Requirements for Establishing an Anthropometic Database. However, the committee is unsure about the accuracy of the calculation for this task, since there was no discussion in the NIOSH-sponsored Anthrotech report and only limited discussion in the protocol, if the 95 percent confidence limits were appropriate for this specific task (Zhuang, 2001; Anthrotech, 2004).

To ensure that the sample adequately captured the variation of measurements within each of the racial groups, Anthrotech oversampled the African American, Hispanic, and “Other” groups—that is, the sample included a larger percentage of these minorities than is found in the general population. During the analysis, each subcategory was then weighted to accurately represent its proportion within the total population. The advantages of this approach are that it provides the needed level of preci-



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