Wednesday, 28 September 2011

Minimum penalties and prosecutorial power [Updated]

A reasonable critique of minimum sentencing laws, and consequently of three-strikes legislation: they let prosecutors force plea bargains for offences without such minima because accused parties fear erroneous conviction and high penalties. Here's the New York Times (HT: all over Twitter)
“We now have an incredible concentration of power in the hands of prosecutors,” said Richard E. Myers II, a former assistant United States attorney who is now an associate professor of law at the University of North Carolina. He said that so much influence now resides with prosecutors that “in the wrong hands, the criminal justice system can be held hostage.” One crucial, if unheralded, effect of this shift is now coming into sharper view, according to academics who study the issue. Growing prosecutorial power is a significant reason that the percentage of felony cases that go to trial has dropped sharply in many places. Plea bargains have been common for more than a century, but lately they have begun to put the trial system out of business in some courtrooms. By one count, fewer than one in 40 felony cases now make it to trial, according to data from nine states that have published such records since the 1970s, when the ratio was about one in 12. The decline has been even steeper in federal district courts.
I wonder whether this effect has contaminated the studies on California's Three Strikes law. Recall that we've seen a big decline in strikeable offences and a smaller increase in non-strikeable offences. The argument has been that some of the decline in strikeable offences has been due to criminals substituting into offences carrying lesser potential sentence. Some of that substitution could just be the exercise of prosecutorial discretion in coercing a guilty plea on a non-strikeable offence where the accused fears the risk of taking a potential strikeable charge to trial. The effect can't be that large though: if it were all that kind of prosecutorial substitution, we'd expect the increase in non-strikeable offences to be larger relative to the decline in strikeable offences. UPDATE: Iyengar's work uses arrest data rather than conviction, and Shepherd's is all on crime rates. So unlikely to be a problem. See comments below, thanks to Lemmus!

I don't know the extent to which plea bargain is used in New Zealand. But this will be something to watch for as our three-strikes legislation becomes binding on more accused.



  1. Which studies of California's three-strikes legislation are you referring to? If memory serves, the studies I've seen use *police* data, to which your reasoning would not seem to apply.

  2. I had thought Iyengar's work was on probability of recidivism and was based on conviction.

  3. I found this paper:

    It is a little disorganized, but my best guess is that the *dependent* variable is based on arrest. P. 22 discusses whether "police officers began charging individuals with more serious crimes after the passage of Three-Strikes law".

  4. Yup, that's the paper I was looking at. Reading the paper again, I honestly have no clue whether his dependent variable is arrest or conviction. He talks about recidivism being the dependent variable; a more natural interpretation of that is "having been found to have committed a crime" rather than "being arrested for a crime, which is correlated with having actually committed a crime in a way that is independent of prior criminal history such that police officers are not more likely to sweep up folks with prior records for any given crime that has been committed".

    Wait... scratch that. There it is at Footnote 18: it's arrest data.

    Ok. So then is there any way that changed incentives facing police induce the perceived substitution effect if the substitution effect comes from arrest data? Recall that there are two substitution effects: from strikeable to non-strikeable offences, and to more severe crimes within the list of strikeable offences. If anything, I'd expect police discretion to attenuate observed effects on the first margin - I'd expect police to be happier to lay the heavier charge in expectation of a plea bargain down to the deserved charge. And, there's no obvious mechanism within the list of strikeable offences. And so I'll have to update the post; thanks!

    Shepherd's work is all on crime rates as dependent variable rather than individual conviction or arrest, though those do show up as explanatory variables via the probability of arrest for a crime & the probability of incarceration given arrest. Not clear that prosecutorial discretion wrecks anything in that setup, other than that the probability of incarceration does go up.