Conference Proceeding

The Heterogeneity Principle

  • Ron Knipling (Safety for the Long Haul Inc.)
  • Anders E af Wählberg (Cranfield University)


The theoretical foundation of the Naturalistic Driving (ND) MixedSafety-Critical Event (SCE) methodology is found in the historical writings of H.W. Heinrich, a 20th century industrial safety engineer. Heinrich espoused the theory that serious accidents, minor ones, and even no-injury operator errors all had identical or highly similar causal mechanisms and that accident consequences were essentially unlinked to causes. This became the basis for today’s ND MixedSCE method, whereby a variety of mostly non-crash avoidance maneuvers (e.g., hard braking, swerves) and other kinematic events (e.g., lane drifts) are aggregated by researchers to form a dependent variable dataset ostensibly representative of important and harmful crashes. This paper examines this approach and finds it to be invalidated by the pervasive causal heterogeneity of crashes and would-be surrogates. Crashes are heterogeneous horizontally by type and vertically by severity. This paper argues instead for the heterogeneity principle as the foundational assumption and guiding tenet for any effort to extrapolate causal evidence from surrogates (e.g., non-crashes or minor crashes) to a different and more important target crash population such as serious crashes.

How to Cite:

Knipling, R. & af Wählberg, A., (2019) “The Heterogeneity Principle”, Driving Assessment Conference 10(2019), 224-230. doi:

Rights: Copyright © 2019 the author(s)

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Published on
26 Jun 2019
Peer Reviewed