Income Inequality, Not Gun Policy or Mental Illness, is the Strongest State-Level Predictor of Mass Shootings in the United States: A Multi-Method Analysis (2018–2024)

Income Inequality, Not Gun Policy or Mental Illness, is the Strongest State-Level Predictor of Mass Shootings in the United States: A Multi-Method Analysis (2018–2024) | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Income Inequality, Not Gun Policy or Mental Illness, is the Strongest State-Level Predictor of Mass Shootings in the United States: A Multi-Method Analysis (2018–2024) Safaa Dabagh This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8905950/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background: Mass shootings are a growing public health crisis in the United States, yet state-level predictors remain poorly understood. Prior research has identified income inequality as a risk factor, but no study has simultaneously examined socioeconomic, mental health, substance use, educational, gun policy, and demographic predictors using multiple analytical methods. This study identifies which state-level characteristics most consistently predict mass shooting rates and evaluates the roles of gun policy and mental illness prevalence. Methods: We compiled corrected Gun Violence Archive data on 3,852 mass shooting incidents (defined as 4 or more persons shot) across all 50 U.S. states and the District of Columbia from 2018 to 2024. We assembled 23 predictor variables from six domains (socioeconomic, mental health, substance use, education/cognitive, gun policy, and demographics) using authoritative sources including the U.S. Census, SAMHSA, FBI, KFF, and NCES. Five complementary analytical approaches were employed: bivariate Pearson correlations, multiple OLS regression, LASSO regularization, Random Forest, and Gradient Boosting. A consensus ranking was derived by averaging variable importance ranks across methods. Results: The Gini coefficient (income inequality) ranked as the most important predictor across all five methods (consensus rank 1.8/21). In the parsimonious OLS model (R² = 0.461, p < .001), the Gini coefficient was highly significant (b = 14.73, p = .007), while poverty rate became non-significant (p = .380) when both were included. Mental health provider density was significantly protective (b = -0.003, p = .030). Gun ownership rate (r = 0.044, p = .762) and gun law strength (r = -0.121, p = .397) showed no significant association. Mental illness prevalence was paradoxically negatively correlated with mass shooting rates (r = -0.307, p = .026). LASSO eliminated all gun policy variables from the model. Conclusions: Income inequality, not gun ownership or mental illness prevalence, is the strongest and most consistent state-level predictor of mass shooting frequency. The paradoxical negative association between mental illness prevalence and mass shootings likely reflects confounding with state-level diagnostic infrastructure. Expanding mental health provider access represents the most actionable policy lever. These findings suggest prevention strategies should prioritize structural determinants of health alongside traditional gun violence interventions. mass shootings income inequality Gini coefficient social determinants of health gun violence mental health state-level analysis LASSO regression public health policy Full Text Additional Declarations No competing interests reported. Supplementary Files AdditionalFile1Dataset.csv AdditionalFile2DataDictionary.csv Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8905950","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":596394788,"identity":"c6fa4842-af43-48a2-9345-f5bc41d27daa","order_by":0,"name":"Safaa Dabagh","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA90lEQVRIiWNgGAWjYFACxgcHGNgYEhgYeBgfMDBYgIQMCGhhNoBpYQYqlSBOCwNUC5sEUVrk25sZD/wos8vj7197rJqnRkKegb15mwQ+LQZnDjMc7DmXXCxx413abZ5jEoYNPMfK8GuRyD9wgLeNObHhxhmz27wNEowNEjlmeLXIz0hmOPi3rT5xPlBLMVCLfYP8G/xaGG4kMxzmbTucuOF8jxkzUEtigwQPfi0gvxyWOXe82PAGj7HknGMSyW08acUWeB3W3sz88U1ZdZ7c+TOGH97U2Nj2sx/eeAOvw+BAIgFCsxGnHAT4DxCvdhSMglEwCkYWAABwaErFevCPWgAAAABJRU5ErkJggg==","orcid":"","institution":"Santa Monica College","correspondingAuthor":true,"prefix":"","firstName":"Safaa","middleName":"","lastName":"Dabagh","suffix":""}],"badges":[],"createdAt":"2026-02-18 05:38:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8905950/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8905950/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":106576870,"identity":"5ed7f9d3-9808-450b-b972-67b1abc93258","added_by":"auto","created_at":"2026-04-10 05:41:56","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3702135,"visible":true,"origin":"","legend":"","description":"","filename":"DabaghBMCManuscriptLaTeX.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8905950/v1_covered_dfee223c-f23a-4c14-9501-b209840d9ff0.pdf"},{"id":103831356,"identity":"09b7a8e7-51ac-4dee-b749-1b88364b1f48","added_by":"auto","created_at":"2026-03-03 12:51:24","extension":"csv","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":30692,"visible":true,"origin":"","legend":"","description":"","filename":"AdditionalFile1Dataset.csv","url":"https://assets-eu.researchsquare.com/files/rs-8905950/v1/f5d67cb3be153e9aa32d1efa.csv"},{"id":103831359,"identity":"cb3c1e16-ef99-4880-b734-3d8ecb1e0e82","added_by":"auto","created_at":"2026-03-03 12:51:25","extension":"csv","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":10804,"visible":true,"origin":"","legend":"","description":"","filename":"AdditionalFile2DataDictionary.csv","url":"https://assets-eu.researchsquare.com/files/rs-8905950/v1/2a1bfd78e77b99492f24169a.csv"}],"financialInterests":"No competing interests reported.","formattedTitle":"Income Inequality, Not Gun Policy or Mental Illness, is the Strongest State-Level Predictor of Mass Shootings in the United States: A Multi-Method Analysis (2018–2024)","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"mass shootings, income inequality, Gini coefficient, social determinants of health, gun violence, mental health, state-level analysis, LASSO regression, public health policy","lastPublishedDoi":"10.21203/rs.3.rs-8905950/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8905950/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eBackground: Mass shootings are a growing public health crisis in the United States, yet state-level predictors remain poorly understood. Prior research has identified income inequality as a risk factor, but no study has simultaneously examined socioeconomic, mental health, substance use, educational, gun policy, and demographic predictors using multiple analytical methods. This study identifies which state-level characteristics most consistently predict mass shooting rates and evaluates the roles of gun policy and mental illness prevalence.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMethods: We compiled corrected Gun Violence Archive data on 3,852 mass shooting incidents (defined as 4 or more persons shot) across all 50 U.S. states and the District of Columbia from 2018 to 2024. We assembled 23 predictor variables from six domains (socioeconomic, mental health, substance use, education/cognitive, gun policy, and demographics) using authoritative sources including the U.S. Census, SAMHSA, FBI, KFF, and NCES. Five complementary analytical approaches were employed: bivariate Pearson correlations, multiple OLS regression, LASSO regularization, Random Forest, and Gradient Boosting. A consensus ranking was derived by averaging variable importance ranks across methods.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eResults: The Gini coefficient (income inequality) ranked as the most important predictor across all five methods (consensus rank 1.8/21). In the parsimonious OLS model (R² = 0.461, p \u0026lt; .001), the Gini coefficient was highly significant (b = 14.73, p = .007), while poverty rate became non-significant (p = .380) when both were included. Mental health provider density was significantly protective (b = -0.003, p = .030). Gun ownership rate (r = 0.044, p = .762) and gun law strength (r = -0.121, p = .397) showed no significant association. Mental illness prevalence was paradoxically negatively correlated with mass shooting rates (r = -0.307, p = .026). LASSO eliminated all gun policy variables from the model.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eConclusions: Income inequality, not gun ownership or mental illness prevalence, is the strongest and most consistent state-level predictor of mass shooting frequency. The paradoxical negative association between mental illness prevalence and mass shootings likely reflects confounding with state-level diagnostic infrastructure. Expanding mental health provider access represents the most actionable policy lever. These findings suggest prevention strategies should prioritize structural determinants of health alongside traditional gun violence interventions.\u003c/p\u003e","manuscriptTitle":"Income Inequality, Not Gun Policy or Mental Illness, is the Strongest State-Level Predictor of Mass Shootings in the United States: A Multi-Method Analysis (2018–2024)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-03 12:51:20","doi":"10.21203/rs.3.rs-8905950/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"dab9ed6e-71cc-4a43-946d-a3a2f5444f98","owner":[],"postedDate":"March 3rd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-10T05:41:24+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-03 12:51:20","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8905950","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8905950","identity":"rs-8905950","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}