This study will describe, estimate, and explore the effectiveness of community-centered safety models (CCSMs)-including co-response, alternative response, and community violence intervention modalities-implemented across U.S. municipalities to prevent community violence among youth and young adults (YYA). Specifically, the investigators will (1) describe CCSM implementation using implementation-science methods, (2) estimate CCSMs' impacts on community-violence outcomes using quasi-experimental methods, and (3) explore operational and contextual factors associated with stronger or weaker effects.

Inclusion Criteria for Jurisdiction/Sites:

1. Intervention modality clarity: A single, identifiable CCSM-Co-Response (CRM), Alternative Response (ARM), or Community Violence Intervention (CVI)-implemented at city/county level.
2. Documented launch date & scope: Public or official documentation specifying program start date, catchment, operating hours, staffing, eligibility, and core activities.
3. Observation window: ≥24 months pre-implementation and ≥12 months post-implementation of outcome data (monthly preferred; annual acceptable for fatal outcomes).
4. Outcomes coverage: Availability of primary outcomes (fatal and nonfatal violent injury) and at least one secondary justice outcome at the jurisdiction level.
5. Data quality: Stable geographic boundaries, consistent reporting practices, and no catastrophic breaks that preclude credible counterfactual fit.
6. Donor comparability: Jurisdiction characteristics and data cadence compatible with a pooled augmented synthetic control design (i.e., can be matched to a synthetic control and included in permutation tests).

Exclusion Criteria:

1. Pilot-only or indeterminate programs: Short-lived pilots, ambiguous or multi-modality rollouts where treatment timing or content cannot be reliably defined.
2. Severe data discontinuity: Major boundary changes, reporting suspensions, coding overhauls, or dataset gaps that undermine time-series integrity (e.g., prolonged outages during system migration) and cannot be addressed with standard remedies.
3. Overlapping major interventions: Concurrent, poorly measured citywide initiatives (e.g., sweeping policy bundles) that coincide with the CCSM start and make identification infeasible.
4. Insufficient pre-period: <24 months pre-implementation data for primary outcomes.
5. Incompatible cadence/aggregation: Outcomes only available at spatial or temporal units that cannot be aligned with other sites or donors.

This protocol does not involve prospective enrollment or direct interaction with individuals. The "participants" in this study are:

1. Jurisdictions/sites (U.S. cities/counties) operating fully implemented community-centered safety models (CCSMs)-co-response, alternative response, or community violence intervention; and
2. Community populations within those jurisdictions, represented only through secondary, de-identified or limited administrative datasets (e.g., violent deaths, nonfatal injury encounters, crime/arrest records) used for population-level analyses.

Youth and young adults (YYA; ~ages 10-34) are a focal analytic subgroup because they bear a disproportionate burden of community violence. No individuals are recruited, contacted, or intervened upon.