The COMPAS risk assessment is a proprietary software tool that scores a criminal defendant’s likelihood of reoffending on a scale of one to ten, and courts and corrections agencies use those scores to inform bail, sentencing, supervision, and parole decisions. Developed by the private company equivant (formerly Northpointe), it stands for Correctional Offender Management Profiling for Alternative Sanctions. It is used mainly at the state and county level, not in the federal prison system, and its accuracy and fairness have been contested since a 2016 investigation found it produced significantly higher false-positive rates for Black defendants than for white defendants.
What COMPAS Scores Actually Measure
The software produces three separate risk scores, each answering a different question a decision-maker faces:
- General Recidivism Risk, the likelihood of any future criminal activity from misdemeanors to felonies.
- Violent Recidivism Risk, the likelihood of future violent offenses specifically.
- Pretrial Release Risk, the likelihood that a defendant will fail to appear in court or commit a new crime while awaiting trial.
Each score is reported as a decile, ranking the individual against a normative group of offenders. A one means the person falls in the lowest ten percent of risk within that comparison group; a ten places them in the highest ten percent. By default, one through four is labeled low, five through seven medium, and eight through ten high. Those cut points are not fixed. A jurisdiction can adjust them: a rural community might lower the violence threshold to seven, while a large metropolitan area might raise it to nine.1Northpointe Inc. COMPAS Risk and Need Assessment System – Selected Questions Posed by Inquiring Agencies
A decile score is a rank, not a probability. A seven means the person scored higher than roughly 60 to 70 percent of the comparison population on that risk dimension. It does not say a seven has a 70 percent chance of reoffending.
What Goes Into the Score
The standard COMPAS Core assessment collects information through a questionnaire of roughly 125 items plus a 14-item current charges table. Administrative staff fill in the fields by pulling data from criminal records and conducting a face-to-face interview with the defendant. The questions divide into two categories.
Static factors are historical and cannot change: prior arrest record, number of convictions, age at first arrest, and prior incarceration history. Court records and police reports supply the verified data. Dynamic factors capture circumstances that can shift: current employment, educational background, substance abuse history, social relationships, and living situation. These are the variables a rehabilitation program can move, which is why they matter for case management as well as for the initial score.
Some of the most scrutinized questions deal with family and neighborhood. The family criminality scale asks whether the defendant’s parents or siblings were ever arrested, whether a parent had a drug or alcohol problem, and whether a parent was ever incarcerated. The social environment scale asks whether crime is common in the defendant’s neighborhood, whether people there feel the need to carry weapons, whether drugs are easy to obtain, and whether gangs are present. Critics argue these items effectively penalize people for circumstances they did not choose.
COMPAS does not ask about race or ethnicity directly. There is no field where a defendant’s race is entered as an input. Critics counter that questions about neighborhood characteristics, family criminal history, and socioeconomic stability can function as proxies for race, given documented disparities in policing, poverty, and incarceration rates. That distinction, between direct racial input and indirect racial correlation, sits at the center of every fairness argument about the tool.
Once the questionnaire is complete, the software runs the data through a proprietary algorithm. The exact weight each variable carries is a trade secret held by equivant. Not every one of the 125-plus items feeds into the risk scores; the general and violent recidivism scales use a smaller subset of variables, including specific subscales and two age variables: age at the current offense and age at first arrest.2Harvard Data Science Review. Setting the Record Straight: What the COMPAS Core Risk and Need Assessment Is and Is Not Because the weighting is hidden, neither the defendant nor the judge can trace exactly how the software arrived at a particular number.
Where the Score Shows Up in Your Case
A COMPAS report can enter the criminal justice process at multiple stages, always as one factor among several rather than a standalone decision.
Pretrial
The Pretrial Release Risk score helps set bail conditions. A high score can lead a court to require electronic monitoring or frequent check-ins. A low score can support release on personal recognizance.
Sentencing
Judges review COMPAS scores as part of a pre-sentence investigation report. The scores help the court gauge whether an individual is better suited for a high-security facility or a community-based alternative. Under the controlling Wisconsin ruling on COMPAS use, scores may not determine the severity of a sentence or whether someone is incarcerated at all. They are permitted for narrower purposes: diverting low-risk, prison-bound offenders to alternatives, assessing whether someone can be supervised safely in the community, and setting conditions of probation.3Justia Law. State v. Loomis
Supervision and Parole
Parole and probation officers use COMPAS scores to build case management plans. A high score generally means more intensive oversight; a low score means lighter monitoring. If the assessment flags substance abuse as a significant factor, an officer can mandate treatment programs as a release condition. The report follows the individual across agencies as a consistent reference point.
Facility Housing
Correctional facilities use the assessment when assigning housing within prisons, identifying individuals at higher risk for violence or victimization so staff can make placement decisions that reduce incidents.
Federal Cases
COMPAS is a state and county tool. The federal prison system does not use it. The Federal Bureau of Prisons relies on the PATTERN instrument, created under the First Step Act.4Federal Bureau of Prisons. PATTERN Risk Assessment Adoption among states varies. Some corrections departments use COMPAS extensively; others use different tools.
How Accurate the Scores Are
Validation studies have found that COMPAS’s general recidivism scale achieves Area Under the Curve (AUC) scores around 0.70 to 0.74 for predicting re-arrest within one to two years. An AUC of 0.70 is generally considered the threshold for good predictive performance; 0.50 is no better than a coin flip.5Center for Court Innovation. Evidence-Based Risk Assessment in a Mental Health Court: A Validation Study of the COMPAS Risk Assessment The tool clears the bar, but not by much.
A 2018 study in Science Advances compared COMPAS to predictions made by untrained volunteers recruited online. COMPAS achieved roughly 65% accuracy in predicting recidivism. Human participants with no criminal justice expertise, given only a defendant’s age, sex, and prior convictions, achieved about 62 to 64% accuracy individually. When the researchers pooled the predictions of 20 volunteers using a majority-rules approach, the crowd hit 67% accuracy, not significantly different from COMPAS.6United States Courts. A Rejoinder to Dressel and Farid: New Study Finds Computer Algorithm Is More Accurate Than Humans at Predicting Arrest and as Good as a Group of 20 Lay Experts Both the software and the humans appear to hit a ceiling near 65%, suggesting a hard limit on how accurately anyone can predict recidivism from the available data.
The tool’s real advantage is consistency. It applies the same formula every time rather than varying with a particular officer’s mood or caseload. Whether that consistency is worth the trade-offs in transparency and fairness is the central policy question.
The Racial Bias Question
In 2016 the investigative newsroom ProPublica published an analysis of COMPAS scores for over 7,000 defendants in Broward County, Florida. Among defendants who did not go on to reoffend, Black defendants had been incorrectly labeled as higher risk at nearly twice the rate of white defendants: 44.9% versus 23.5%. The tool made the opposite error for white defendants, who were more likely to be labeled lower risk and then commit another crime: 47.7% versus 28.0% for Black defendants. Overall, COMPAS correctly predicted recidivism about 61% of the time regardless of race.
Equivant argued that ProPublica used the wrong fairness metric. The company’s position is that the correct standard is predictive parity: when the tool says someone is high risk, that prediction should be equally accurate for all racial groups. By that measure, equivant said, COMPAS performs equitably. ProPublica focused instead on error-rate balance: whether incorrect classifications are distributed evenly across racial groups.
The uncomfortable mathematical reality is that when the base rate of recidivism differs between two groups, a tool cannot simultaneously achieve both predictive parity and equal error rates. Satisfying one metric requires violating the other. That is not specific to COMPAS. It applies to any prediction system operating on populations with different base rates. The debate is about which type of unfairness is more acceptable, which is a values question rather than a statistical one.
What the Law Allows: State v. Loomis
The most significant court ruling on COMPAS came from the Wisconsin Supreme Court in 2016. In State v. Loomis, the court held that a trial court’s consideration of a COMPAS risk assessment at sentencing does not violate a defendant’s due process rights, provided specific safeguards are followed.3Justia Law. State v. Loomis The decision is binding only in Wisconsin, but its ground rules have influenced how other jurisdictions treat algorithmic risk tools.
The court required that any pre-sentence investigation report containing a COMPAS score include a written advisement with five specific cautions:7Supreme Court of Wisconsin. State v. Loomis Opinion
- The developer has invoked trade secret protections to prevent disclosure of how factors are weighed or how scores are calculated.
- The scores are based on group data and can identify groups of high-risk offenders, but not a particular high-risk individual.
- Some studies have raised questions about whether the tool disproportionately classifies minority offenders as higher risk.
- The tool compares defendants to a national sample, and cross-validation for the local population may not have been completed; risk tools must be regularly re-normed for accuracy.
- COMPAS was not developed for use at sentencing. It was intended for the Department of Corrections to make treatment, supervision, and parole decisions.
That last warning is easy to overlook. The tool’s own developer designed it for corrections case management. Courts have repurposed it for sentencing, which is a higher-stakes decision with different constitutional requirements.
Loomis drew clear lines around permissible uses. A COMPAS score cannot determine whether a defendant is incarcerated or how long the sentence will be. A judge cannot use a high score to bump a sentence from two years to five if no other evidence supports the increase. The score may be used only as one factor among many, and the sentencing court must explain what additional factors support the sentence imposed. Permissible uses include diverting low-risk offenders away from prison, assessing whether someone can be safely supervised in the community, and setting terms and conditions of probation.
Challenging a COMPAS Score
Under Loomis, a defendant has the right to review the COMPAS report included in the pre-sentence investigation and to challenge the accuracy of the input data. In that case the court and the defendant had access to the same copy of the risk assessment, including a list of questions and the defendant’s recorded answers. If a criminal history entry is wrong or an interview response was recorded incorrectly, the defendant can identify and correct that error.7Supreme Court of Wisconsin. State v. Loomis Opinion
What a defendant cannot challenge is the algorithm itself. The court explicitly held that the proprietary computational method is shielded from review. A defendant can argue that the data fed into the machine was wrong, but cannot argue that the machine processes correct data unfairly. The only recognized avenue for dispute is factual accuracy of inputs.
In practice, that means verifying every factual entry in the report: prior arrest counts, conviction records, interview responses, and charge classifications. Errors in these fields directly change the output score. If your jurisdiction uses the updated COMPAS-R Core version, ask for the Long Report option, which shows the defendant’s response on each item, the points that response earned, all other possible responses and their corresponding point values, and the norm set used for comparison.8equivant. Why Was the COMPAS-R Core Created and How Does It Differ from the Standard COMPAS Core That report makes it easier to trace how a particular answer affected the score, even though the underlying statistical model that converts point totals into decile ranks still belongs to equivant.