Death Penalty: A Look at the Numbers
Posted by Michael Dickens on July 25, 2010
One of the most controversial issues right now is the death penalty. It is unique among popular political arguments in that arguments may rely heavily on either the numbers or on philosophical points. The numbers are often overlooked in favor of the philosophical points, and even when people do address the numbers they often get them wrong.
Finding statistics regarding the death penalty isn’t too difficult as long as you have an internet connection, or access to a library. There are plenty of helpful websites out there with tables of statistics — even the clearly biased ones can be useful. The government has what is probably the most reliable and least biased data, but it’s a lot harder to sift through.
I did some research and put together some of the most important numbers.
Supporters of the death penalty argue that it is a deterrent to crime. What do the numbers say?
Every year from 1990 until today, states without the death penalty have had lower murder rates, with an average reduction of about 25%. This appears to show that the death penalty is not an effective deterrent, but correlation does not imply causation. It’s possible that states with higher murder rates are the slowest to ban the death penalty.
A more accurate statistic would be one that looks at the crime rate of a state before and after it abolished the death penalty, i.e. did the crime rate go up?
Not a whole lot of states have abolished the death penalty. Some of them abolished it too long ago for there to be easily-accessible statistics, and others abolished it too recently for the data to be worth anything. The only really prime states are Massachusetts, North Dakota, and the District of Columbia.
This table contains useful statistics. Data is from this site. The table gives the average murder rate from 1960 to 2008, the average murder rate before abolition of the death penalty, and the average murder rate after abolition.
This still doesn’t take into account other factors that would contribute to changing the murder rate. The second table shows the ratio of murder to violent crime; a higher ratio means that murder is disproportionately represented among violent crime. If the death penalty does act as a deterrent from murder, then the murder rates should go up more than the violent crime rates, so this ratio should increase. It’s possible that there are other factors that affect murder rates and not other forms of violent crime, but this ratio can still serve to remove some of the bias.
Execution of Innocents
One of the main arguments of opponents of the death penalty is that innocent people are mistakenly executed. What do the numbers say?
Wikipedia has its own list of wrongfully executed people, although few people on the list were conclusively innocent.
Conclusion: Information on the execution of innocents is inconclusive.
The California Commission on the Fair Administration of Justice did a study on California’s death penalty and produced a report. It found that
. . . [C]onfinement on death row adds $90,000 per year to the cost of confinement beyond the normal cost of $34,150. Thus, just the enhanced confinement costs for the 670 currently on California’s death row totals $63.3 million. This figure increases each year as the population of California’s death row grows.
These figures do not take into account the additional cost of a trial ending in a death sentence, which are estimated to cost approximately $1 million more. However, it is necessary to put the above numbers in context. As the CCFAJ report explains, California has one of the least efficient justice systems and inmates in California on average spent much longer on death row than in most other states. The costs of capital punishment will almost definitely be lower in other states.
A Kansas State study confirmed the increased costs:
[T]he estimated median cost of a case in which the death sentence was given was about 70% more than the median cost of a non-death penalty murder case. That figure was $1.2 million compared to about $740,000.
These are three of the most important statistics regarding the death penalty, and the relevant context. When you see statistics, remember to consider exactly what they mean. Correlation does not imply causation.
If there are any other subjects around capital punishment that you’d like to see the statistics for, let me know and I’ll see what I can do.