Think of a number, then multiply by 2.6
The Herald has a story about police being arrested: 67 over 2 2/3 years. That’s about 25 per year. The rate this year so far is a bit lower than in the previous two years, but well within the margin of error.
The Police Association says this proves we don’t need an independent complaints process, since the police already do a good job in catching their own when they stray. Of course, the figures don’t show anything of the sort, unless there is some independent reason to believe that 25/year is the number that should be arrested. The Police Association also says that many of the arrests would have ‘not guilty’ results. This could be true, and it’s a pity that neither the Herald nor the Police Association provided any actual information on convictions.
The Herald also quotes a survey from October, purporting to show that confidence in police has fallen. I covered this at the time. It doesn’t.
The arrest counts are not evidence one way or the other on how well the police are policed. They are easier to obtain than relevant evidence would be, but that’s not much consolation.
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. See all posts by Thomas Lumley »