Statistics rule our world in many ways, but their value is surely taken too far when they tell us the rate of successful criminal prosecutions is too high. That is what the New Zealand Law Society said when Statistics New Zealand reported the conviction rate to be its highest in at least 35 years. Last year, 83.2 per cent of people charged in our courts were convicted. Prosecution success rates have risen in 10 of the past 11 years.

"It's heading the wrong way," said Law Society president Jonathan Temm. "Our level should be constantly around the 75 per cent mark. Anything over 80 per cent (means) people are pleading guilty to things that in the past they would not have been convicted of."

Really? How was that figure pre-determined to be the benchmark of justice? It is reminiscent of school exams in the days of "scaling". If much more than 50 per cent of pupils passed the qualification, it meant the exam was not hard enough.

In that event, the education authorities used to scale back all marks so only the desired proportion passed. If more pupils than usual had been smart enough, or had studied hard enough, to pass that year, well, tough luck for some of them. At least, there is no suggestion some of each year's convictions should be quashed to reduce the rate to 75 per cent retrospective, but that is a small mercy. Why can we not simply celebrate a rising success rate for those who bring charges to court?


One reason, says the Criminal Bar Association, is police and Crown Solicitors are laying "inappropiately serious charges" for the sake of plea bargaining - manipulating defendants, in other words, to plead guilty to a lesser charge. The police reportedly acknowledge this has happened but they blame the prosecutors' inexperience.

One barrister writing to the Herald noted the rise in the rate of convictions since a public defender service was set up in 2009, and blamed the volume of work they face. Previously, private lawyers had been accused of defending hopeless cases to get more fees, conceded Dr Richard Keam. "That may be so. But at least everybody got their day in court even if the poor old taxpayer got stuck with the bill." The poor old taxpayer is probably happier if defence lawyers on state salaries no longer have an incentive to prolong hopeless cases with expensive trials.

The statistics also show fewer people are going through the courts. The number has dropped by almost 40 per cent since 2009, which corresponds with declines in overall crime in recent years, not just in New Zealand but in comparable countries.

That is another statistic many of us are reluctant to take at face value, suggesting it means fewer people are reporting crime because police are deprived of resources to investigate them. We are in danger of precluding the possibility of genuine improvement, just as the old school exams did. The justice system is not perfect. It has produced some highly publicised false or suspect convictions in recent times. But if fewer crimes are being committed and fewer cases are coming to court, perhaps prosecutions can be more thorough and successful. Good news can happen.