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Projecting Fatalities in Crashes Involving Older Drivers, 2000-2025

Projecting Fatalities in Crashes Involving Older Drivers, 2000-2025

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APPENDIX C. NOTES<br />

C.1. REGIONAL VMT AND HEALTH INDEX COMPUTATIONS FOR 1983<br />

DATA<br />

The 1983 NPTS did not conta<strong>in</strong> a variable identify<strong>in</strong>g the respondent’s region of<br />

residence. Therefore, <strong>in</strong> order to obta<strong>in</strong> the average health score and vehicle miles of travel<br />

numbers needed for the aggregate crash rate model, we took the percent difference between<br />

the regional and national figures for the two variables <strong>in</strong> 1990 and adjusted the national<br />

average for each respective gender/age average <strong>in</strong> 1983 by these regional variation measures.<br />

C.2. STARTING VALUES FOR VMT VALUES OF SOUTHERN MEN<br />

The 1995 start<strong>in</strong>g values used <strong>in</strong> the projections were slightly modified due to the<br />

<strong>in</strong>consistencies <strong>in</strong> historical VMT for Southern men. These <strong>in</strong>consistencies <strong>in</strong>volved two<br />

cases where an older group had a higher average VMT <strong>in</strong> 1995 than a younger group. The<br />

two cases <strong>in</strong>volved 70-74 Southern men hav<strong>in</strong>g less VMT than their 75-79 year old<br />

counterparts, and the 80-85 group hav<strong>in</strong>g a lower average than the 85+ group. In order to<br />

account for this, a simple iterative proportional fitt<strong>in</strong>g procedure was used. Given the simple<br />

nature of the problem, this iterative proportional fitt<strong>in</strong>g amounted to tak<strong>in</strong>g the average of the<br />

two groups affected <strong>in</strong> each case and us<strong>in</strong>g that average as the start<strong>in</strong>g po<strong>in</strong>t for both groups.<br />

In Table C.1 below are the orig<strong>in</strong>al values observed from the 1995 NPTS for each group,<br />

along with their modified numbers used <strong>in</strong> projections.<br />

Table C.1. Average VMT per Person of Southern Men, 1995 NPTS and Adjusted<br />

Numbers<br />

Age 1995 NPTS Base Used<br />

<strong>in</strong> Projections<br />

70-74 10431 10909<br />

75-79 11388 10909<br />

80-84 4681 5336<br />

85+ 5991 5336<br />

GM Project G.6 C - 1<br />

October <strong>2000</strong>

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