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Suggested Citation:"Appendix A - Weighting Factors." National Academies of Sciences, Engineering, and Medicine. 2015. Naturalistic Driving Study: Descriptive Comparison of the Study Sample with National Data. Washington, DC: The National Academies Press. doi: 10.17226/22196.
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Page 33
Page 34
Suggested Citation:"Appendix A - Weighting Factors." National Academies of Sciences, Engineering, and Medicine. 2015. Naturalistic Driving Study: Descriptive Comparison of the Study Sample with National Data. Washington, DC: The National Academies Press. doi: 10.17226/22196.
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Page 34

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33 a p p e n D i x a In Chapter 2 and Chapter 4, figures depicting comparisons between study recruitment areas, their respective states, and the nation as a whole include a series labeled “Recruitment Site Counties Weighted by Nominal Site Size.” Data in these series are weighted based on each site’s size, as determined by the number of DAS kits nominally allocated to that site, as outlined in Table A.1. Similarly, figures in Chapter 4 that compare the SHRP 2 NDS sample and other relevant populations include a series labeled “SHRP 2 Sample Weighted According to Age/Gender” derived by weighting the data associated with the study sample accord- ing to the distribution of licensed drivers across the United States in 2012, the last full year of data collection. The weighting factors used to derive this series are presented in Table A.2. Weighting Factors Table A.1. Weighting Factor for Each Site Based on Original Nominal Number of DAS Kits Managed Site No. of DAS Kits Site Size–Based Weighting Factor New York 450 3 Florida 450 3 Washington 450 3 North Carolina 300 2 Indiana 150 1 Pennsylvania 150 1

34 Table A.2. Weighting Factors for SHRP 2 Sample by Age and Gender Gender Age No. of Licensed Drivers in 2012a 2012 Licensed Drivers Weighting Factor for Age and Gender M ≤19 4,506,199 0.0212742 F ≤19 4,323,609 0.0204122 M 20–24 8,836,224 0.0417167 F 20–24 8,644,805 0.0408130 M 25–29 9,142,229 0.0431614 F 25–29 9,214,424 0.0435023 M 30–34 9,088,323 0.0429069 F 30–34 9,242,363 0.0436342 M 35–39 8,667,787 0.0409215 F 35–39 8,758,112 0.0413480 M 40–44 9,532,858 0.0450056 F 40–44 9,568,468 0.0451737 M 45–49 9,893,354 0.0467076 F 45–49 9,943,257 0.0469432 M 50–54 10,298,601 0.0486208 F 50–54 10,459,435 0.0493801 M 55–59 9,503,385 0.0448665 F 55–59 9,738,712 0.0459775 M 60–64 8,128,957 0.0383777 F 60–64 8,379,398 0.0395600 M 65–69 6,311,060 0.0297952 F 65–69 6,515,908 0.0307623 M 70–74 4,349,210 0.0205331 F 70–74 4,557,392 0.0215159 M 75–79 3,040,690 0.0143554 F 75–79 3,255,371 0.0153689 M 80–84 2,096,580 0.0098982 F 80–84 2,338,480 0.0110402 M 85+ 1,589,660 0.0075050 F 85+ 1,889,979 0.0089228 a Federal Highway Administration 2014.

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TRB’s second Strategic Highway Research Program (SHRP 2) has released Report S2-S31-RW-1: Naturalistic Driving Study: Descriptive Comparison of the Study Sample with National Data that provides technical support to users of the SHRP 2 Naturalistic Driving Study (NDS) data. Specifically, the report provides guidance for analysts with weighting SHRP 2 NDS data so they may make comparisons with the U.S. population.

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