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Evaluation of the Use and Effectiveness of Wildlife Crossings (2008) / Chapter Skim
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Appendix D - Illustrating Regression to the Mean
Pages 137-138

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From page 137...
... This random fluctuation also suggests that a site with a higher collision count is not necessarily a stronger candidate for safety improvement than a site with a lower count. The upshot of this phenomenon is that the crash count by itself is not good enough for estimating the safety of a site for use in identifying candidate improvement locations and in estimating the safety effect of potential or implemented countermeasures.
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From page 138...
... Crashes 3 yr s Prior Number of Site s Crashes 19971999 Crashes 2000- 2002 % difference 6 8 61 41 -32.8 5 8 40 27 -32.5 4 21 84 41 -51.2 3 55 165 84 -49.1 2 147 294 149 -49.3 1 792 792 343 -56.7 0 11941 0 951 infinite increase Table 44. Data for California illustrating regression to the mean.
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  • crash data
  • collision count
  • amounts shown
  • predictive guides

  • simply compares
  • sophisticated predictive
  • infinite increase
  • random fluctuation
  • safety effect

  • random fluctuations
  • crash count
  • term counts
  • fewer crashes
  • considerable increase

  • rows based


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