Citation

Hauer E. IATSS Res. 1990; 14(2): 7-15.

Copyright

(Copyright © 1990, International Association of Traffic and Safety Sciences, Publisher Elsevier Publishing)

DOI

unavailable

PMID

unavailable

Abstract

To manage unsafety we need to know how much safer is "A" then "B". Unfortunately, in spite of extensive experience with many measures, too often their impact on unsafety is not known. It is truly difficult estimate differences in unsafety. To answer the question of "how much safer" one has to guess at "what would have been". What method of guessing is good is an empirical question. In this light I examine the problem of choosing a comparison system. Next I argue that the question is not about whether a null hypothesis can be rejected but about what is the magnitude of the effect on unsafety of some intervention. The harm of repeated significance testing is illustrated in the case of the right turn on red controversy. Another cause of ignorance is that the management of road safety is the responsibility of public bodies. People who lead and served these bodies seldom find it in their interest to find out what effect on unsafety their programs have had.