Sample image of the dataset
Introduction:
The National Registry of Exonerations is an interesting dataset because it is a snapshot of mistakes that were made by the criminal justice system, and were then repaired. At the time of writing this post, there were 3,487 exonerations recorded. Carrying out an exoneration can take years and extensive resources, so many innocent individuals who were wrongfully convicted of a crime are never exonerated. Researchers estimate that "wrongful convictions occur in 6% of criminal convictions leading to imprisonment in an intake population of state prisoners" [1]. Roughly, with 1.2 million individuals in state prisons in 2022, [3] the 6% figure implies that there are 72,000 innocent individuals currently incarcerated. Thus, it is likely that there should be many more exonerations than there currently are in the US.
About the dataset (from their website [2]):
The National Registry of Exonerations is a project of the Newkirk Center for Science & Society at University of California Irvine, the University of Michigan Law School and Michigan State University College of Law. It was founded in 2012 in conjunction with the Center on Wrongful Convictions at Northwestern University School of Law. The Registry provides detailed information about every known exoneration in the United States since 1989-cases in which a person was wrongly convicted of a crime and later cleared of all the charges based on new evidence of innocence. The Registry also maintains a more limited database of known exonerations prior to 1989.
A word of caution:
Be cautious with what you claim about summary statistics about this dataset. For example, 25% of the exonerations had false or misleading forensic evidence as a contributing factor. This does not mean that 25% of all wrongfully convicted individuals had faulty forensic evidence, or that forensic testimony is wrong 25% of the time. It just means that, out of the cases that have led to an exoneration and are recorded in this dataset, a quarter of them involved faulty forensic testimony.
Data access:
To access the data, go to this website: https://www.law.umich.edu/special/exoneration/Pages/Spread-Sheet-Request-Form.aspx
Fill out the information and if you click "I agree", the spreadsheet will download to your computer.
The codebook is the glossary on this page: https://www.law.umich.edu/special/exoneration/Pages/glossary.aspx
Using the dataset for teaching:
This is a simple and small dataset that has been interesting to my students. We have used it to visualize summary statistics and do exploratory data analysis. It is a useful example for thinking about what we should and should not conclude from data.
References:
[1] Loeffler, Charles E., Jordan Hyatt, and Greg Ridgeway. "Measuring self-reported wrongful convictions among prisoners." Journal of Quantitative Criminology 35 (2019): 259-286.
[2] The National Registry of Exonerations, Online at: https://www.law.umich.edu/special/exoneration/Pages/about.aspx, last accessed: April 5, 2024.
[3] E. Ann Carson, Prisons Report Series: Preliminary Data Release, NCJ Number 307411, September 2023. Online at: https://bjs.ojp.gov/library/publications/prisons-report-series-preliminary-data-release, last accessed: April 5, 2024.