Methodology
Our research methodology is guided by Hamline University Institutional Review Board protocols and a commitment to “no notoriety” for mass shooters—focusing on prevention rather than perpetrators.
Definition
What is a Mass Public Shooting?
The Violence Project focuses on mass public shootings, defined as incidents with four or more murdered victims using firearms (excluding the offender) in a public location, not attributable to underlying criminal activity.
Key Distinctions
- Excludes domestic homicides occurring in private residences
- Excludes gang-related violence and criminal activity motivations
- Focuses on the shooter as the primary unit of analysis
Research Approach
Four Phases of Research
Database Creation
Creation of a comprehensive database of mass public shooters from 1966 onward, coded on 100+ life history variables including mental health, trauma, interest in past shootings, and situational triggers.
Community Analysis
Examination of community socio-ecological factors where shootings occur, including crime rates, social inequality, community mobility, mental health resources, and gun store availability.
In-Depth Interviews
Life history interviews with incarcerated living mass shooters and follow-up interviews with stakeholders including family members, first responders, survivors, and experts.
Dissemination
Public dissemination of findings through our website and development of evidence-based prevention strategies to help communities, practitioners, and policymakers.
Data Sources
Primary Sources
- Journals, manifestos, and suicide notes
- Social media posts and blogs
- Audio and video recordings
- Interview transcripts
- Personal correspondence
Secondary Sources
- Media coverage and documentary films
- Biographies and peer-reviewed articles
- Court transcripts and police reports
- Medical and school records
- Autopsy reports
Community Data
- U.S. Census Bureau data
- FBI Uniform Crime Reports
- Google Maps for location analysis
Coding Process
Work on the database began in Summer 2017. Our rigorous coding process ensures accuracy and reliability across all variables.
Each shooter is investigated by two independent coders
Datasets are merged and compared for consistency
Discrepancies are reconciled by Principal Investigators with fact-checking
Database is reviewed again by original coders
Database Manager conducts final comprehensive check
Principal Investigators approve publication
Understanding the Data
Our databases use specific terminology to distinguish between different types of missing or negative data. Understanding these distinctions is important for accurate interpretation of the research.
"No evidence of"
Our researchers investigated this variable and found no evidence in available sources. This does not mean the answer is definitively "No" — only that no supporting evidence was found in court records, media reports, interviews, or other available documentation.
Example: "No evidence of mental health issues" means no evidence was found, not that the individual was confirmed to have no mental health issues.
"Unknown"
Information about this variable could not be determined from available sources. This may be due to privacy restrictions, sealed records, limited media coverage, or gaps in documentation.
Example: Unlike "No evidence of," which implies the variable was investigated, "Unknown" indicates the information was not available for review.
"N/A" (Not Applicable)
This variable does not apply to the case in question.
Example: A field specific to workplace incidents would be marked N/A for a school shooting.
Important Caveats
We have taken every step possible to find and verify sources and to rigorously fact-check the data, but the end result is not perfect. Users should be aware of the following limitations:
Purposive Sample
This is a purposive sample with no comparison group, limiting generalizability.
Low Base Rate
The low base rate of mass shootings makes predictive modeling problematic.
Mental Health Complexity
While rates of mental illness are high among mass shooters, the majority of people with mental disorders are not violent.
Missing Data
Some data is missing due to privacy laws, varying media coverage, and source availability.
Interpretation
Data is subject to interpretation and source quality variations.
Version History
Our database is continuously updated as new incidents occur and additional data becomes available.
The Violence Project: How to Stop a Mass Shooting Epidemic
Launched at the American Society of Criminology Annual Meeting in San Francisco, CA
Research Team
Principal Investigators
Dr. Jillian Peterson
Dr. James Densley
Database Managers
Jaycee Johansson (versions 6–10)
Stasia Higgins (versions 1–5)
Funding Acknowledgment: This project was originally supported by National Institute of Justice Award 2018-75-CX-0023. The opinions, findings, and conclusions or recommendations expressed are those of the authors and do not necessarily reflect those of the Department of Justice.
Explore the Data
Ready to explore our research? Access our databases, download datasets, or ask questions directly.