Short answers, pulled from the story.
COMPAS is case management and decision support software that U.S. courts use to assess the likelihood that a defendant will become a repeat offender. It has been used in New York, Wisconsin, California, and Florida's Broward County, among other jurisdictions.
COMPAS was created in 1998 by Northpointe, Inc., which merged with other justice technology firms to form equivant in January 2017. Equivant owns and develops the software today.
In July 2016, the Wisconsin Supreme Court ruled that judges may consider COMPAS risk scores during sentencing. The court required that any such score come with warnings describing the tool's limitations and cautions.
COMPAS is controversial because its algorithm is a trade secret that cannot be examined by the public or the people it scores, which critics say violates due process. A 2016 ProPublica investigation also found the software was racially biased against black defendants, while Northpointe said it predicted recidivism accurately regardless of race.
COMPAS uses separate scales for pretrial misconduct, general recidivism, and violent recidivism, each drawing on different factors such as criminal history, employment status, and history of violence. The violent recidivism scale combines factors including current age, age at first arrest, history of violence, vocational education, and history of noncompliance through a weighted formula.
A 2018 study by Dressel and Farid found COMPAS somewhat more accurate than individual predictions made by people with little or no criminal justice expertise, but less accurate than predictions made by groups of such individuals. A later review found that algorithms performed better than humans under conditions closer to the real world, including when the base rate of rearrest was low.