The MASTLE: Obtaining Legitimacy Through Fair, Impartial, and Objective Decision-Making

Trust and legitimacy are built on fairness and integrity. When law enforcement personnel are trustworthy, honest, and concerned about the well-being of the people they encounter, long-term relationships can be established. However, when the public perceives the police to be partial and arbitrary, anger and resentment proliferate. One of the greatest concerns specific to policing is the use of unguided discretion. Expressly, the question is whether officers are making decisions in a fair, objective, and unbiased manner. It is widely accepted that the use of discretion is necessary in law enforcement; one cannot reasonably conduct an arrest for every violation of the law. Instead, it is the perception of uneven enforcement of laws that leads to divisiveness, strife, and even violence. However, the use of an objective, validated tool to assist during arrest and detention proceedings can promote fairness and maintain or restore public trust and legitimacy. This is especially true when juveniles are involved.

MASTLE and Evaluating Youth Risk Factors

The Massachusetts Arrest Screening Tool for Law Enforcement (MASTLE) is an objective, validated screening tool that estimates the likelihood that a youth taken into law enforcement custody for a criminal offense will be arrested for the commission of another offense in the future or will fail to appear for arraignment.1 This information will give supervisors and commanders additional information to make appropriate pre-processing decisions using objective, empirical data. It can lead to structured, accurate, and consistent decision-making, thus, eliminating the perception of bias and unevenness in enforcement of juvenile laws. The MASTLE (and tools like the MASTLE) are not intended to eliminate officer discretion; rather, the tool provides additional information to help guide discretion based on objective, tested, and validated criteria.

The MASTLE’s development was guided by several principles based on the nature of adolescent development and on research regarding what does and doesn’t work in juvenile justice. First, arrest should be the last measure in a continuum of police processing decisions, particularly for lower-risk youth. There is evidence that deeper penetration into the juvenile justice system is associated with higher rates of reoffending rather than prevention of reoffending.2 Youth who have been detained or incarcerated are also more likely to abuse alcohol and drugs, suffer from depression, and attempt suicide.3 Low-risk youth are highly unlikely to benefit from juvenile justice interventions, but high-risk youth can.4 Furthermore, the severity of the offense alone is not a sufficient indicator of the individual’s risk to public safety or the likelihood they will commit another crime.5 Validated risk assessment tools comprising characteristics of youths, their families, and their environment that have a known association with future offending are much better predictors of who will go on to commit more crime.

The MASTLE was developed and validated in Massachusetts as a method to objectively determine youths’ risk factors in association with criminality and offending. The MASTLE is a valid measure of youths’ risk of rearrest and failure to appear for both girls and boys from the primary race and ethnicity groups on which it was tested (i.e., white, black, and Hispanic). An added benefit of using the tool is that it promotes consistency in law enforcement processing decisions by minimizing the bias that might occur due to an arrestee’s background, behavior, or demographics.

The applicable risk factors are rated and added up into a total risk score. The risk score does not guarantee whether a person will or won’t be rearrested or fail to appear for arraignment. It does, however, represent how high a risk the person is for those actions. The higher the score, the greater the risk for the individual’s rearrest or failure to appear for arraignment. This allows law enforcement to facilitate and manage pre-arraignment detention and booking decisions using objective, standardized, empirical data. The MASTLE is a weighted checklist that can be filled out, and the risk score can be readily calculated given sufficient background information and behaviors. The MASTLE, like all other risk tools designed in this manner, requires validation when used in new jurisdictions to determine whether the scoring must be adjusted in order to maintain its validity. In other words, one wants to ensure the cutoff score to identify a high-risk youth is actually separating the group of youth who is most likely to be rearrested in jurisdictions outside of Massachusetts. For example, a youth who was arrested before the age of 26 or has prior delinquency arraignments, open warrants, or limited ties to the community based on length of residency has a higher likelihood or rearrest.

Sorting juvenile offenders by risk requires valid risk assessment instruments, which are critical tools for facilitating the matching of the right services to the right youth at the right time. Juvenile justice systems need to consider risk in conjunction with the juveniles’ mental health to ensure that appropriate services are provided. However, mental health problems should not be treated in isolation if criminogenic risk factors—factors likely to lead to criminality—also exist

Risk screening also needs to be applicable across racial groups to ensure uniform applicability and fairness. Black youth in the United States, for example, are arrested at rates 4.9 times greater than white youth.6 Hispanic youth are arrested at rates 1.5 times greater than non-Hispanic white youth.7 Research indicates that many law enforcement officers equate black males with criminality, and this tendency is not limited to police.8 Neuroscience research indicates that a tendency toward racial bias is fairly pervasive, and, in fact, many people are not aware of their own biases.9 The use of an objective screening tool that has been rigorously tested for accuracy across racial and ethnic groups can counter officers’ conscious or unconscious biases. It can also mitigate the realities of disproportionate minority contact and confinement in the juvenile justice system.

Use of a structured tool to make arrest decisions can also help conserve resources by sorting out and diverting low-risk youth away from the justice system. One of the primary reasons for arrest is to remove threats to public safety, either in the present or near future. However, many youths who engage in illegal acts are not threats to public safety and are at minimal risk for repeat behavior. Youths often get into trouble as a consequence of being easily influenced by peers or through reward-seeking behaviors, as opposed to having malicious intent or antisocial attitudes.

Use of structured tools also provides an opportunity to demonstrate to the public that law enforcement agencies are striving to promote fairness and impartiality. Variables such as disrespect of law enforcement, background, and demographics are not appropriate predictors of repeat offending behavior or the likelihood that one will not appear in court for arraignment. Use of these variables to make arrest decisions is counterproductive to the law enforcement mission and a waste of valuable resources such as time and manpower.

Criticality of Fair and Equitable Enforcement

According to a recent study on citizen’s complaints against law enforcement officers, the number one complaint identified was that officers exhibited, “unreasonable, unfair behavior.”10 According to the literature on procedural justice and police legitimacy, the treatment rendered by officers is more important than the actual outcome. In other words, if an offender is treated with respect and fairness when placed under arrest, the treatment, rather than the actual arrest, is more significant. The current environment involving ambushes of law enforcement officers underscores the importance of public perception, which can be improved when officers engage in neutral, fair, and equitable treatment of community members, including those they arrest. It also highlights the importance of communication. Officers should explain what they are doing and why they are doing it so there is no misinterpretation and the public can understand the rationale behind specific police actions (even though they might not agree with the actions). When objectivity and impartiality are a critical part of detention and arrest decisions, fairness and equity become more readily apparent.

Fair and impartial policing increases police legitimacy, which means that the public believes that police actions are morally justified and appropriate.11 The benefits of mutual trust and respect between law enforcement and the public include greater public deference to officers during community-police interactions, increased compliance with the law, and greater cooperation with law enforcement efforts to manage crime.12 In other words, the public accepts that the police are doing the right thing for the right reason at the right time. The effects of an improper or unwarranted arrest can permanently damage an agency’s ability to effectively serve a community. Law enforcement and the public are mutually dependent upon one another to effectively control and deter crime; without   the support of the public, an agency’s capabilities are severely hindered.

The perception of unevenness and bias in the enforcement of the law has led to the erosion of public confidence in the legitimacy of law enforcement. Even if the public supports its local department, the perception that law enforcement in general is biased is widespread. This has most greatly affected the men and women of law enforcement. The recent ambushes of law enforcement officers in the United States are unprecedented in their scope. In order to avert these incidents, the public must understand that the overwhelming majority of arrest decisions are completed after thoughtful consideration of the facts and circumstances available to well-trained, well-meaning officers.


Law enforcement officers and leaders will be able to more readily collaborate with the public when the public recognizes that equitable and balanced enforcement is taking place. The use of an evidence-based tool to assist with arrest and detention decisions of juveniles ensures objectivity and fairness, and it instills public confidence that the officers are appropriate and reasonable. The positive outcomes associated with this type of law enforcement can have far-reaching effects for the community, the police, and the young people officers encounter.


1 Gina Vincent, Michael Gropman, Finesee Moreno-Rivera, and Rachael Perrault, MASTLE: Massachusetts Arrest Screening Tool for Law Enforcement (National Youth Screening & Assessment Partners, 2015).

2 Uberto Gatti, Richard E. Tremblay, and Frank Vitaro, “Latrogenic Effect of Juvenile Justice,” Journal of Child Psychology & Psychiatry 50, no. 8 (August 2009): 991–998.

3 Barry Holman and Jason Ziedenberg, The Dangers of Detention: The Impact of Incarcerating Youth in Detention and Other Secure Facilities (Washington, DC: Justice Policy Institute, 2006).

4 Mark W. Lipsey, “The Primary Factors That Characterize Effective Interventions with Juvenile Offenders: A Meta-Analytic Overview,” Victims and Offenders 4 (2009): 124–147. 

5 Edward P. Mulvey, et al., “Trajectories of Desistance and Continuity in Antisocial Behavior Following Court Adjudication among Serious Adolescent Offenders,” Development and Psychopathology 22, no. 2 (May 2010): 453–475.

6 Melissa Sickmund, Juveniles in Corrections, Juvenile Offenders and Victims National Report Series, Department of Justice, Office of Juvenile Justice and Delinquency Prevention, June 2004.

7 Christopher Hartney and Linh Vuong, Created Equal: Racial and Ethnic Disparities in the US Criminal Justice System (Oakland, CA: National Council on Crime and Delinquency, 2009).

8 Ronald Weitzer and Steven Tuch, “Race, Class, and Perceptions of Discrimination by the Police,” Crime & Delinquency 45, no. 4 (October 1999): 494–507.

9 Anthony G. Greenwald and Linda Hamilton Krieger, “Implicit Bias: Scientific Foundations,” California Law Review 94, no. 4 (2006).

10 Wesley G. Skogan, “Partnerships for Prevention? Some Obstacles to Police Community Cooperation” (presentation, 22nd Cropwood Round-Table Conference—Preventing Crime and Disorder: Targeting Strategies and Community Responsibilities, Cambridge University, UK, September 14-16, 1994).

11 Tom R. Tyler, What Are Legitimacy and Procedural Justice in Policing? And Why Are They Becoming Key Elements of Police Leadership? (Washington, DC: Police Executive Research Forum, 2014).

12 Jason Sunshine and Tom R. Tyler, “The Role of Procedural Justice and Legitimacy in Shaping Public Support for Policing,” Law & Society Review 37, no. 3 (September 2003): 513–548.