Is drink driving down?

The Dom Post reports:

The number of us prepared to drink and drive has plummeted in the past five years, but there are still pockets of the country bucking the trend.

Convictions for drink-driving, or refusing to supply a sample, decreased in all but five of the country’s 64 district courts between 2009 and 2013, the latest available Ministry of Justice figures show.

The only courts to enter more convictions last year than in 2009 were Waipukurau, Ruatoria, Thames, Oamaru and Westport.

Waipukurau and Ruatoria saw the biggest increases, of 33 per cent and 54 per cent respectively, and while the other three had marginal increases, they were a long way from the national decrease of 25 per cent, the figures, released to The Dominion Post under the Official Information Act, show.

I’m not sure you can conclude on this data that drink driving has plummeted. It may have, but the number of convictions will be dependent on how much time is spent on checking motorists. I presume it has not decreased, but we don’t know.

The better measure would be the detection rate – what proportion of motorists stopped, are found to have excess blood alcohol?