The Evidence
Trying to make sense of the CVI evidence base? The “evidence” pages break down the language of evaluation and summarize what researchers have learned about community-based violence intervention. You will find FAQs, research guides, evidence reviews, and individual study summaries designed to help you understand what works, for whom, under what conditions, and where important questions remain.
What You’ll Find Here
-
FAQs
Straightforward answers to the questions practitioners ask most often when starting or running a CVI program.
-
Key Research Terms & Evaluation Vocabulary
Structured learning opportunities that build skills for outreach workers, supervisors, and program leadership alike.
-
Quick Guides
Short, practical overviews you can read in minutes and put to use the same day.
-
Evidence Synthesis Resources & Websites
Organizations offering hands-on support, coaching, and expertise to strengthen your program’s design and daily operations.
Frequently Asked Questions
Key Research Terms for Understanding CVI Evidence
CVI research includes many study designs and types of evidence summaries. Knowing the key terms will help you ask better questions, understand study findings, and use evidence wisely.
Why this matters: Not all evidence is the same. Understanding these terms helps you evaluate the quality of research and apply it to build safer, stronger communities.
Core Terms in Study Design
Causal inference means deciding whether a program or strategy actually caused a change in outcomes. In CVI, this usually means asking whether a decline in shootings, retaliatory violence, or violent injury happened because of the program itself, rather than because of other factors such as citywide trends, policing changes, seasonality, or unrelated interventions happening at the same time.
The counterfactual is the estimate of what likely would have happened without the program. Because we cannot observe the same person, group, or neighborhood both receiving and not receiving the intervention at the same time, researchers use control groups or comparison groups to estimate that “what would have happened otherwise” condition.
Outcomes are the changes observed during or after a program, such as fewer shootings, stronger school engagement, improved mental health. Program impact refers to the part of those changes that can be attributed to the program itself. Put simply, outcomes describe what changed; impact asks whether the program caused the change. To determine impact, one needs a counterfactual or a causal research design.
A process evaluation examines how a program was implemented (e.g., Was the program delivered as intended?) whereas an impact evaluation examines whether the program itself caused changes in outcomes. Both types of evaluation matter. Process evaluations help explain how a program worked, while impact evaluations help determine whether it made a difference.
A control group is a group of people, places, or communities that does not receive the program and is selected through random assignment. Because chance determines who gets the intervention and who does not, researchers can make a stronger claim that differences were caused by the program.
A comparison group does not receive the program but is not randomly assigned. Instead, it is selected to resemble the program group on important factors such as prior shootings, poverty and demographics. Researchers may use matching or statistical adjustments to make the comparison more credible.
Random assignment means using chance to determine who receives the program and who does not. This helps reduce bias because the groups should be similar before the program begins. Random assignment is often seen as the strongest design for estimating impact, but in CVI it is not always practical or ethical, especially when interventions are designed for entire neighborhoods or social networks.
Internal validity refers to how confidently we can say that the program itself caused the observed results. A study has stronger internal validity when it does a better job of ruling out other explanations for what happened.
Core Terms in Evidence Synthesis
A systematic review is a review that uses clear and explicit methods to identify, select, and critically assess all relevant studies on a focused question. Rather than summarizing studies informally, it follows a structured process to synthesize the best available evidence.
Why it matters: High-quality systematic reviews are valuable because they assess the total body of evidence, not just one study.
A meta-analysis is a statistical method that combines findings from multiple studies to estimate the overall size and direction of an effect. When the studies are sufficiently comparable, a meta-analysis can provide a stronger summary than any one study alone.
Why it matters: Meta-analyses often sit near the top of the evidence pyramid (hierarchy) because they pool results quantitatively, but they are only as strong as the studies they include.
A scoping review maps the main concepts, types of evidence, and gaps in research on a topic. It is especially useful when a field is still developing, when definitions vary, or when researchers want to understand what kinds of studies exist before asking narrower questions about effectiveness.
Why it matters: Scoping reviews are helpful for understanding the shape of a field, but they usually do not provide the same level of evidence about effectiveness as a systematic review or meta-analysis.
A summary review is a broader overview of the literature that highlights major findings, lessons, or themes from prior studies. Summary reviews can be very useful for practitioners because they often translate research into more accessible takeaways, but they are much less formal than systematic reviews and meta-analyses and may not use transparent methods for selecting and assessing studies.
Why it matters: Summary reviews can orient readers to a field, but they generally provide a weaker basis for judging effectiveness than systematic reviews or meta-analyses.
Quick Guides
Evidence Synthesis Resources & Websites
Evidence websites use different standards, terminology, outcome measures, and cutoffs for rating programs. A program may receive different classifications across clearinghouses, and the absence of a program from a registry does not necessarily mean that it is ineffective—it may mean that it has not yet been evaluated rigorously, reviewed by that clearinghouse, or studied using the outcomes required for inclusion. The resources listed below, presented in no particular order, have different uses and some are not regularly updated.
1. Campbell Collaboration Crime and Justice
Host: Campbell Collaboration, an international research network
Campbell produces rigorous systematic reviews and meta-analyses of interventions intended to prevent or control crime and delinquency or improve policing, courts, corrections, probation, and other justice-system functions. This is one of the strongest sources when you want a synthesis of all qualifying evaluations rather than a profile of one named program. Campbell Collaboration
2. What Works Centre for Crime Reduction / Crime Reduction Toolkit
Host: College of Policing, United Kingdom
This resource summarizes systematic-review evidence on crime-reduction approaches and presents information about impact, mechanisms, settings, implementation, cost, and the quality of the evidence. It is particularly strong for policing, situational prevention, place-based strategies, and criminal-justice interventions.
3. Washington State Institute for Public Policy Benefit-Cost Results
Host: Washington State Institute for Public Policy
WSIPP conducts meta-analyses and benefit-cost analyses across adult criminal justice, juvenile justice, prevention, child welfare, behavioral health, education, and other policy areas. Its program pages report effect sizes, estimated benefits, costs, benefit-cost ratios, and the probability that benefits will exceed costs. The dollar estimates are tailored to Washington State, although the underlying evidence reviews are useful elsewhere.
4. Results First Clearinghouse Database
Host: Evidence-to-Impact Collaborative, Penn State University
Results First brings together information from multiple established clearinghouses and translates their different rating systems into a more consistent evidence continuum. It contains more than 4,000 programs spanning criminal justice, behavioral health, education, public health, and other social-policy fields. This is especially useful when you want to search several evidence registries from one place.
5. Blueprints for Healthy Youth Development
Host: Institute of Behavioral Science, University of Colorado Boulder
Blueprints is one of the most selective registries of youth programs. It reviews interventions intended to reduce antisocial behavior, delinquency, violence, substance use, and other risks while promoting healthy youth development. It places considerable emphasis on evaluation quality, replication, sustained effects, and readiness for dissemination.
6. Youth Endowment Fund Toolkit
Host: Youth Endowment Fund, United Kingdom
The YEF Toolkit synthesizes evidence about approaches intended to prevent violence affecting children and young people. It rates broad approaches—such as mentoring, focused deterrence, sports programs, cognitive behavioral therapy, street outreach, and social-skills programming—rather than simply listing branded programs. It summarizes estimated impact, evidence quality, implementation considerations, and cost.
7. National Gang Center
Host: Office of Juvenile Justice and Delinquency Prevention and the Institute for Intergovernmental Research
The National Gang Center provides research summaries, program and strategy information, implementation tools, training, and guidance on comprehensive gang prevention, intervention, and focused enforcement. It is the main source for the OJJDP Comprehensive Gang Model and is particularly useful for communities building coordinated gang- and group-violence strategies.
8. California Evidence-Based Clearinghouse for Child Welfare
Host: California Department of Social Services–supported clearinghouse
Although primarily focused on child welfare, this California-based registry includes many interventions relevant to violence-exposed youth, behavioral problems, family functioning, trauma, mentoring, and justice-involved young people. It rates research support and also provides extensive guidance on selecting and implementing programs.
9. Title IV-E Prevention Services Clearinghouse
Host: Administration for Children and Families, U.S. Department of Health and Human Services
This clearinghouse reviews programs serving children and families and rates them as well-supported, supported, promising, or not currently meeting criteria. Its principal focus is child-welfare prevention, but it includes behavioral-health, family, parenting, substance-use, and youth-service models relevant to violence prevention and youth justice partnerships.
10. What Works Clearinghouse
Host: Institute of Education Sciences, U.S. Department of Education
The What Works Clearinghouse reviews educational interventions and studies. Its relevance to youth violence is strongest in areas such as school climate, social-emotional learning, student behavior, dropout prevention, mentoring, and programs for youth displaying aggression or disruptive behavior.
11. Safer Cities research
Safer Cities is a public-facing research and policy website that curates reporting, studies, interviews, and examples of alternative public safety strategies being used in cities across the United States. Their site has a new AI-powered intelligence tool (Safer Cities IQ) that lets you search the full Safer Cities archive and surface relevant examples, evidence, and insights in seconds—from mobile crisis response and crisis stabilization centers to violence intervention strategies, safety ambassador programs, and public opinion on public safety.
12. CrimeSolutions and OJJDP Model Programs Guide
Host: Office of Justice Programs, U.S. Department of Justice
CrimeSolutions reviews and rates evaluated programs and broader practices across criminal justice, juvenile justice, victim services, school safety, gun violence, and youth mentoring. Program profiles summarize the intervention, evaluation design, outcomes, and strength of the evidence. The site currently displays a notice that it is no longer being updated (since 2025).
The OJJDP Model Programs Guide (MPG) is very similar to CrimeSolutions, but focuses more on juvenile justice, delinquency prevention, youth intervention, reentry, and child protection. The MPG is now presented as an archived resource (since 2025), and much of its program-rating content overlaps with CrimeSolutions.