Prevention Portfolios, Residual Mechanisms, and Cross-Level Fit

Abstract

Complex crime problems are frequently addressed through combinations of interventions. Yet the presence of several interventions does not establish that they form a coherent prevention portfolio, cover the relevant crime process, operate compatibly, or support claims of sufficiency or optimality. This paper develops a claim-bounded architecture for deciding when portfolio analysis is warranted and how multiple independently profiled interventions should be combined. It introduces structural single-intervention insufficiency as the condition under which an otherwise defensible intervention remains unable to support the bounded prevention claim because central mechanisms, carriers, scales, temporal dependencies, protective requirements, or interaction conditions remain materially uncovered. The paper establishes an explicit admission gate to portfolio analysis and defines the claim-relative coverage matrix, the prospective residual set, and the final frozen pre-outcome prevention portfolio. It further analyses complementarity, duplication, redundancy, robustness, interference, incompatibility, overload, sequencing, bottlenecks, cross-level transmission, institutional-bearer compatibility, feasibility, reproducibility, and portfolio misalignment. Portfolio claims are limited through a bounded ladder ranging from provisional static coverage to conditionally optimal within declared constraints. Empirical effectiveness and comparative superiority remain downstream questions. This is Paper 5 of 6 in the Prevention Fit Programme. Its output is the frozen pre-outcome portfolio and prospective residual record inherited by process-sensitive evaluation.