Wrongful conviction—the conviction of a factually innocent person—is becoming an important policy issue in criminal justice and criminology research. A wrongful conviction is deemed worse than a wrongful acquittal, also an error of justice, because it implicates the very governmental apparatus relied on to provide justice. They are very difficult to detect and no official records are kept. Estimates of wrongful felony convictions range from 0.005 to 0.03, or from about 5,000 to 30,000 (and 2,000 to 12,000 prison admissions) each year. Many factors, including eyewitness identification errors, false confessions, forensic error, perjury, ineffective defense lawyers, and prosecutorial misconduct regularly appear in false conviction cases, suggesting a causal influence, although scientific evidence of cause and effect is limited. Impediments to reform include inherent problems like cognitive bias and policy impediments like not videotaping confessions, conducting suggestive lineups, and underfunding indigent defense. Half the states provide compensation for wrongful convictions.