December 2, 2016

Crash statistics

From the Herald

Obviously there isn’t research giving ‘the exact time you will crash your car’.  What you might hope for is the time at which you (more precisely, the average NZ driver) are at highest risk.  We don’t even get that.

The comparisons are for totals, and as the story admits, more crashes happen in peak times because more people are driving.  It’s worse than that, though. The story says

…22,000 collisions occur annually in the afternoon peak up to 6pm. This then drops to just 2000 crashes a year at 11pm and a mere 800 at 1am.

The 22,000 is over 3-hour periods and I think the 2000 and 800 are for single-hour periods — I can’t tell for sure, because there’s no link to the original source, and I can’t find it on the IAG website.

Perhaps more relevantly for the New Zealand Herald, you have to read down to paragraph 11, which begins “Across most states…” to get the first solid indication that this story is about another country.

It’s from, which explains why the handling of numbers isn’t up to local standards.


Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »