Citation

Elvik R. Accid. Anal. Prev. 2002; 34(5): 631-635.

Affiliation

Institute of Transport Economics, Oslo, Norway. rune.elvik@toi.no

Copyright

(Copyright © 2002, Elsevier Publishing)

DOI

unavailable

PMID

12214957

Abstract

This paper discusses the importance of confounding in observational before-and-after studies of road safety measures. The importance of the approach taken to controlling for confounding factors is shown by means of examples. It is shown that the size of the effect on accidents attributed to a road safety measure can be profoundly affected by which confounding factors are controlled for in an evaluation study, and the way this is done. Simple before-and-after studies, not controlling for any confounding factors should never be trusted and are likely to overstate the effects of road safety measures.