Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users (2007) / Chapter Skim
Currently Skimming:
4 Data Analysis and Fit-Test Panels
4 Data Analysis and Fit-Test Panels
Pages 53-80
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 53... ...
workforce, versus the population of current and potential respirator-wearing workers, may have an impact on the final distributions. Using these weights as multipliers against the data in each cell, the Anthrotech investigators then derived basic summary statistics for each of the dimensions measured and provided summary tables of those analyses.
|
From page 54... ...
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.
|
From page 55... ...
To adjust for undersampling or oversampling in some of the strata, as compared to the target population, stratum-specific weights are used and the 24 cells become "adjustment cells." In the NIOSHsponsored Anthrotech study, the weights are computed as the relative frequency of a given stratum in the census (Ni/N: where Ni is size of ith stratum and N is total count over all strata) divided by a relative frequency of the same stratum (ni/n: where ni is the sample count in ith stratum and n is the sum of counts over all strata)
|
From page 56... ...
The ratio of these two fractions then gives the weight = 1.517127. (These fractions, and hence the weights, are computed from the following sample and reference population information, should ni/n not be equal to 271/3,997 and Ni/N = 14,281,917/178,189,001 the total sum used instead of gender sum used)
|
From page 57... ...
57 DATA ANALYSIS AND FIT-TEST PANELS TABLE 4-2 Sample Size by Race Male Age Group Female Age Group 18- 30- 45- 18- 30- 45Race 29 44 65 Total 29 44 65 Total White 271 611 485 1,367 151 194 174 519 African 101 255 278 634 51 213 325 589 American Hispanic 155 182 75 412 53 36 37 126 Other 24 47 59 130 52 65 103 220 Total 551 1,095 897 2,543 307 508 639 1,454 NOTE: Final sample reflects congruence with original sample target, which eliminated those under 18 and over 65 years of age; however, later measurements include those aged 66. Category labeled "Other" includes Asian, Pacific Island, Native American, and mixed race.
|
From page 58... ...
, July 13, 2006. TABLE 4-4 The Sample Fraction Based on Gender-Specific Total Male Age Group Female Age Group Race 17-29 30-44 45-66 Total 17-29 30-44 45-66 Total White 0.106567 0.240267 0.190720 0.537554 0.103851 0.133425 0.119670 0.356946 African 0.039717 0.100275 0.109350 0.249312 0.035076 0.146492 0.223521 0.405089 American Hispanic 0.060952 0.071569 0.029493 0.162013 0.036451 0.024759 0.025447 0.086657 Other 0.009438 0.018482 0.023201 0.051121 0.035763 0.044704 0.070839 0.151307 Total 0.216673 0.430594 0.352733 1.000000 0.211142 0.349381 0.439477 1.000000 NOTE: Data contained in this table is a ratio of Table 4-2 sample sizes for each category to total sample aggregate.
|
From page 59... ...
Zhuang, NPPTL, July 13, 2006. TABLE 4-6 Weighting Factors Based on Gender-Specific Totals Male Age Group Female Age Group Race 17-29 30-44 45-66 Total 17-29 30-44 45-66 Total White 1.517127 1.069367 1.474251 1.301782 1.501958 1.890047 2.406211 1.950184 African American 0.835652 0.424766 0.312287 0.440902 0.999516 0.324193 0.181555 0.303962 Hispanic 0.808882 0.691441 0.933585 0.779704 1.123734 1.822352 1.149698 1.330964 Other 2.333071 1.339092 0.741733 1.251487 0.597215 0.565743 0.264959 0.432360 Total 1.228517 0.868017 1.020745 1.000000 1.199948 1.059252 0.856832 1.000000 NOTE: Weighting factors determined as the fraction of race to age group in the U.S.
|
From page 60... ...
could have a great impact on all subsequent analyses, and therefore raises a concern about the analyses presented in the NIOSHsponsored Anthrotech study. In particular, since one of the main arguments for updating the LANL face panel relies on the high proportion of the population no longer covered by the LANL face panel when fitting the weighted Anthrotech data into it, it remains to be seen whether this conclusion holds when using the revised set of weights.
|
From page 61... ...
However, there was no discussion of whether the number of boxes is appropriate, or whether there may be problems of fit for persons near the edges of the boxes. The updated full- and half-face panels proposed by the NIOSHsponsored Anthrotech study were based on the menton-sellion length and bizygomatic breadth facial dimensions.
|
From page 62... ...
129.5 119.5 109.5 99.5 124.5 136.5 148.5 160.5 120.5 132.5 144.5 156.5 Bizygomatic Breadth (mm) FIGURE 4-1 Revised full-face panel.
|
From page 63... ...
Equal number in cells seems a reasonable compromise between these competing objectives. In testing the fit of masks for certification, NIOSH assigns test subjects to cells based on their facial dimensions as measured at the time of the fit test.
|
From page 64... ...
Std Dev (mm) Std Dev 120.3 6.1 106.3 6.1 Menton-Sellion LANL Length NIOSH 122.7 7.1 113.4 6.1 Difference 2.4 7.1 Bizygomatic LANL 142.3 5.2 129.0 5.8 Breadth NIOSH 143.5 6.9 135.0 6.5 Difference 1.2 6.0 Lip Length LANL 52.3 3.8 43.8 4.2 NIOSH 51.1 4.2 48.0 4.0 Difference 1.2 4.2 SOURCE: Zhuang, November 3, 2005.
|
From page 65... ...
Recommendation 4-2: Include Large and Small Faces in Panel. NIOSH should develop an expanded anthropometric face panel that includes the larger-sized faces de scribed in the NIOSH-sponsored Anthrotech study, while retaining the small-sized subjects from the LANL face panel.
|
From page 66... ...
NIOSH should perform a study in which it compares the range of quantitative fit provided for specified respirators on subjects representing the LANL face 1 The CEASAR study collected information from 4,000 ethnically, racially, and gender diverse volunteers in 10 geographic regions in the United States.
|
From page 67... ...
The committee is uncertain if the bivariate face panels that the NIOSH-sponsored Anthrotech study provide are an acceptable means of determining if tested respirators can be relied on to fit the group of workers for which the sizes are designed. One potential problem with the proposed face panels is that, although Anthrotech chose face length and face width as the foundation for the face panels, there is no consensus within the literature as to which anthropometric features have the greatest impact on respirator fit.
|
From page 68... ...
. In 1992, Oestenstad and Perkins found significant correlations between four facial dimensions (menton-subnasale, binocular breadth, nasal root breadth, and nose width)
|
From page 69... ...
Nasal root breadth was also significantly narrower in Koreans." The researchers found no correlation between fit and any facial dimensions for men in quarter-face respirators. On the other hand, fit in women was significantly correlated with bitragion-subnasale arc.
|
From page 70... ...
Quantitative Fit Test The committee notes that the term total inward leakage is unique to NIOSH, as the rest of the scientific community uses the term quantitative fit test. The term may have been adapted to describe filtering facepiece studies wherein the filter element cannot be altered, and therefore, leakage measurements include both the filter element and the facepiece.
|
From page 71... ...
. Conclusion The ultimate utility of the data collected in the NIOSH sponsored Anthrotech study is limited because the study did not include the collection of fit-testing data along with facial measurements.
|
From page 72... ...
Principal Component Analysis Although the face panels that the NIOSH-sponsored Anthrotech study developed were, in the end, simply updates of the original LANL face panels that used new and more comprehensive survey data, NIOSH did develop a separate face panel derived from a principal component analysis (PCA) of the anthropometric data collected in Anthrotech's survey (Box 4-2)
|
From page 73... ...
To perform the principal component analysis of the survey data, Zhuang evaluated the various anthropometric measurements using such methods as expert opinion and regression analysis in order to zero in on the variables that were best correlated with fit (Zhuang, November 3, 2005)
|
From page 74... ...
. Figure 4-5 shows the overall facial size trends of the individuals in the survey plotted against these two principal components.
|
From page 75... ...
The NIOSH-sponsored Anthrotech study paid little attention to these matters, yet different mean forms will undoubtedly have different variances, different fits, and local aspects of these will very likely vary in magnitude (as pertains to fit around a specific part of the face)
|
From page 76... ...
• Anthrotech selected its variables based on published studies that reported correlations between certain facial features and fit, but unless the populations used in those studies were similar to the population of interest to NIOSH, choices to include or exclude variables for the PCA based on these studies may be inappropriate. • If the variable selection step were not suspect, then the five-class categorization scheme based on PCA might well be a better way to classify subjects into various respirator sizes than a similar five-category classification based on a bivariate panel.
|
From page 77... ...
The two proposed face length- and width-based face panels developed from the NIOSH-sponsored Anthrotech study and the related PCAderived face panels described above are based on similar assumptions. Working from the total sample population, a small number of cells are defined that together include most of the target population (there are 10 cells for each of the length- and width-based face panels and 5 for the PCA panel)
|
From page 78... ...
Two examples of this approach are illustrated in Figure 4-6, which are notional illustrations of how the total sample distribution of facial measurements may be divided into cells representing equiprobable, or equally-sized, subsets of the total distribution. The contours in the background are the nonparametric density contours that were computed from the Anthrotech data.
|
From page 79... ...
NIOSH should examine the potential effects of a non linear relationship between respirator fit and facial dimensions. REFERENCES Anthrotech.
|
From page 80... ...
Presentation to Committee for the Assessment of the NIOSH Head-and-Face Anthropometric Survey of U.S. Respirator Users: Respirator fit test panels representing the current U.S.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.