Friday, July 30, 2010

On The Rate of Wrongful Conviction: Chapter 2.3

As I have mentioned seven times previously, I am preparing a monograph on the rate of wrongful conviction. Each chapter will deal with one estimate of that rate, beginning with zero and ending beyond 10%. I am posting the draft chapters here, as I write them.  I have so far posted the following: 

Chapter 0.027: The Scalia Number
Chapter 0.5: The Huff Number
Chapter 0.8: The Prosecutor Number
Chapter 1.0: The Rosenbaum Number
Chapter 1.3: The Police Number
Chapter 1.4: The Poveda Number
Chapter 1.9: The Judge Number

Now, for the first time, we break the 2% barrier. The numbers will begin to climb rapidly after this post.

Chapter 2.3
The Gross Number

In December 2008, Samuel Gross wrote:
Since 1973, 128 U.S. criminal defendants who were sentenced to death have been exonerated. This is a startlingly high number … Most likely, this extraordinary number of capital exonerations is caused in part by a higher underlying error rate among capital convictions and in part by a higher rate of detection of those errors after conviction. It is well known that more resources are devoted to capital defense than to other cases, before and after conviction, but it is hard to believe that better review alone explains the capital exoneration rate. If that were the whole story, it would mean, for example, that if we had reviewed prison sentences with the same level of care that we devoted to death sentences, there would have been approximately 87,000 non-deathrow exonerations from 1989 through 2003 rather than the 266 that were reported in a comprehensive study in 2005.
Gross realized he could compare capital murder exonerations to capital murder convictions to determine a wrongful conviction rate, at least for capital murder. All he had to do was divide the number of exonerations by a properly related number of convictions and, voila, a wrongful conviction rate. He wasn’t going to simply guess, or have others guess for him. He was going to find a good numerator and a good denominator and he was going to divide.

Gross knew, however, he had to be careful in his selection of both the numerator and the denominator. He was careful to include in his numerator only those people who were likely to be factually innocent. He intentionally excluded those who might have been removed from death row for technical reasons, those who were merely re-sentenced, and those who were re-tried and found guilty once again.
As we use the term, “exoneration” is an official act -- a pardon, a dismissal, or an acquittal -- declaring a defendant not guilty of a crime for which he or she had previously been convicted … Very likely, however, some defendants we count as “exonerated” did in fact participate in the crimes for which they were convicted. In our estimation, the probability of innocence is high for all of these exonerated defendants -- for many, innocence is beyond dispute -- and the number of misclassifications low enough to make these exonerations a useful proxy for innocence. … And, of course, the set of exonerated defendants does not include innocent defendants who were executed, nor those who remain on death row, nor the undetected innocent defendants among the thousands of defendants who have been removed from death row but remain in prison.
He was also careful when he selected his denominator. He realized he couldn’t simply divide all exonerations by all convictions because exonerations don’t happen overnight.
[W]e know that 7,534 people were sentenced to death from 1973 through 2004. In the same period, 111 defendants were exonerated after being sentenced to death for murder under a post-Furman capital sentencing statutes, or 1.5 percent of all death sentences.

That figure -- 1.5 percent -- is not the final word on exonerations for the cohort of defendants who have been sentenced to death since 1973, let alone a reasonable estimate of the rate of false capital convictions. As time passes, some defendants in this group who have not yet been exonerated will be.
To account for the lag between conviction and exoneration, Gross realized that most exonerations (95%) occurred within 20 years of conviction. He would therefore make sure his denominator accounted for that 20 year lag. He would divide all the exonerations from 1973 through 2004 (54) by all the convictions from 1973 through 1984 (2,394) to arrive at a wrongful conviction rate of 2.3 percent.
Of the post-Furman death row inmates who were exonerated between 1973 and 2004, 95 percent had been freed within 20 years of their conviction (106/111). Overall, 2,394 death sentences were pronounced in U.S. courts from 1973 through 1984. By 2004, the process of identifying exonerations for these 20 to 30-year-old death sentences was largely complete. It resulted in 54 exonerations -- almost exactly half of all capital defendants who were exonerated through 2004 -- or an exoneration rate of 2.3 percent (54/ 2,394).
He checked his number by assuming a 15-year lag instead of a 20-year lag.  He ended up with the same number: 2.3 percent.
Eighty-one percent of capital exonerations occurred within 15 years of sentencing (90/111). By the end of 2004 there had been 86 exonerations among the 3,792 capital defendants who had been sentenced to death through 1989, at least 15 years earlier, also an exoneration rate of 2.3 percent Two additional defendants who were sentenced to death before 1990 were exonerated in 2005, but judging from the pattern of previous cases, we have probably seen almost all the capital exonerations that we will see for defendants sentenced to death through 1989.
He naturally concluded that he had arrived at a good estimate of the wrongful conviction rate, at least for capital murder trials in the United States.
In other words, a good estimate of the long-term … capital exonerations rate in the United States is 2.3 percent.
Solid as his math seems to be, I disagree with Samuel Gross on this number. I will await Chapter 11.3 to make my case.

1. When I write of Samuel Gross, I write actually of Samuel R. Gross and Barbara O’Brien. Together they wrote “Frequency and Predictors of False Conviction: Why We Know So Little, and New Data on Capital Cases”, Journal of Empirical Legal Studies Volume 5, Issue 4, 927-962, December 2008

2. At the time their article was published, Samuel Gross and Barbara O’Brien were Assistant Professors of Law at Michigan State University College of Law.

3. Gross and O’Brien recognize that the wrongful conviction rate for capital murder cases is not necessarily equal to the rate for all cases. They are careful to limit their conclusion to capital murder cases. “All things considered, we believe that 2.3 percent -- the long-term rate of exoneration of death row inmates -- is a conservative estimate of the rate of wrongful death sentences.”