A miscarriage of justice occurs when a grossly unfair outcome occurs in a criminal or civil proceeding, such as the conviction and punishment of a person for a crime they did not commit. Miscarriages are also known as wrongful convictions. Innocent people have sometimes ended up in prison for years before their conviction has eventually been overturned. They may be exonerated if new evidence comes to light or it is determined that the police or prosecutor committed some kind of misconduct at the original trial. In some jurisdictions this leads to the payment of compensation. Academic studies have found that the main factors contributing to miscarriages of justice are: eyewitness misidentification; faulty forensic analysis; false confessions by vulnerable suspects; perjury and lies stated by witnesses; misconduct by police, prosecutors or judges; and/or ineffective assistance of counsel (e.g., inadequate defense strategies by the defendant's or respondent's legal team). Some prosecutors' offices undertake conviction integrity reviews to prevent, identify, and correct wrongful convictions. Prevalence There are two main methods for estimating the prevalence of wrongful convictions. Exoneration The first is the number of exonerations where the guilty verdict has been vacated or annulled by a judge or higher court after new evidence has been brought forward proving the 'guilty' person is, in fact, innocent. Since 1989, the Innocence Project has helped overturn 375 convictions of American prisoners with updated DNA evidence. However, DNA testing occurs in only 5 to 10% of all criminal cases, and exonerations achieved by the Innocence Project are limited to murder and rape cases. This raises the possibility that there may be many more wrongful convictions for which there is no evidence available to exonerate the defendant. Studies cited by the Innocence Project estimate that between 2.3% and 5% of all prisoners in the U.S. are innocent. However, a more recent study looking at convictions in the state of Virginia during the 1970s and 1980s and matching them to later DNA analysis estimates a rate of wrongful conviction at 11.6%. A 2014 study published in Proceedings of the National Academy of Sciences made a conservative estimate that 4.1% of inmates awaiting execution on death row in the United States are innocent. Self-report The second method for estimating wrongful convictions involves self-report. Researchers ask prisoners whether they have ever confessed to a crime which they did not commit. Self-report allows examination of any and all crimes where wrongful conviction