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Prosecution certainty, crime prevention and procedural safeguards: an error-constrained deterrence frontier
Abstract
In a deterrence model with investigation errors, we prove the following. (i) Deterrence depends on correct-sanction certainty $p_C$ and wrongful-sanction probability $p_I$ only through $D(s)(p_C-p_I)$. Wrongful sanctions therefore erode deterrence one-for-one with correct ones. (ii) If the disutility of sanction severity is concave, for example discounted prison time, then the deterrence elasticity of certainty strictly exceeds that of severity. This gives a precise version of "certainty over severity". (iii) With an ROC investigation frontier $p_C=R(p_I;z)$, the error-constrained optimum binds the safeguard constraint iff $R'(\bar p_I)$ exceeds an explicit cost-adjusted ratio. (iv) Sanction counts by regime do not identify $(p_C,p_I)$ or the deterrence elasticity. An independent validation sample, or an exclusion restriction, is required, and we give the identifying moment.1. Model
A potential offender with gain $g\sim F$ offends iff $g>D(s)\,(p_C-p_I)$. Here $D(s)$ is the disutility of sanction severity $s$, and $p_I$ is the probability of a wrongful sanction when innocent, which is suffered whether or not one offends. The crime rate is $c=1-F(D(s)(p_C-p_I))$. Harm is $h\,c$, and institutional cost is $K(z)$. A policy $z$ maps to $(p_C,p_I)$ on the investigation frontier $p_C=R(p_I;z)$, with $R$ concave and increasing in $p_I$, as in signal-detection theory: a more lenient evidentiary threshold raises both rates.Proposition (Wrongful sanctions erode deterrence): $\partial c/\partial p_I=-\partial c/\partial p_C=f(\cdot)D(s)>0$. Holding $p_C-p_I$ fixed, deterrence is unchanged.
Proof: Differentiate; the threshold depends on $(p_C,p_I)$ only through the difference. This is the observation of [png]. ∎
2. Certainty versus severity
Proposition: Let $\Delta=p_C-p_I>0$ and $\varepsilon_x=\partial\log(1-c)/\partial\log x$. If $D$ is concave with $D(0)=0$, then $\varepsilon_{p_C}\ge\frac{p_C}{\Delta}\,\varepsilon_s\ge\varepsilon_s$, with strict inequality if $D$ is strictly concave. For $D(s)=(1-\delta^s)/(1-\delta)$ (discounted years), $\varepsilon_s/\varepsilon_{p_C}=\frac{\Delta}{p_C}\cdot\frac{s\,\delta^s\log(1/\delta)}{1-\delta^s}<\frac{\Delta}{p_C}$.
Proof: Write $1-c=F(D(s)\Delta)$ and $\phi=f/F$ evaluated at the threshold. Then $\varepsilon_{p_C}=\phi\,D\,p_C$ and $\varepsilon_s=\phi\,D'(s)\,s\,\Delta$. Concavity with $D(0)=0$ gives $sD'(s)\le D(s)$. ∎
3. The safeguard-constrained optimum
The planner solves $\min_{p_I}\ h[1-F(D\cdot(R(p_I)-p_I))]+K(p_I)$ subject to $p_I\le\bar p_I$, with procedural safeguards encoded as membership of $z$ in $\mathcal Z_{\rm proc}$, which restricts the attainable frontier $R$.Proposition: Assume $F$ is differentiable and $R$ concave. The constraint binds iff $h\,f\,D\,(R'(\bar p_I)-1)>K'(\bar p_I)$ at $p_I=\bar p_I$. The unconstrained optimum therefore exceeds the safeguard when, at the safeguard, loosening the threshold adds correct sanctions faster than wrongful ones ($R'>1$) by enough to cover marginal cost. If $R'(\bar p_I)\le1$, the safeguard never binds: further leniency weakly reduces deterrence.
Proof: The objective's derivative in $p_I$ is $-hfD(R'-1)+K'$. The KKT conditions on $[0,\bar p_I]$ give the claim. Concavity of $R$ makes $R'-1$ decreasing. ∎
Thus a low wrongful-sanction cap is compatible with deterrence as long as the frontier is steep at low $p_I$. Investment in investigation quality shifts $R$ upward, raising $p_C$ at fixed $p_I$. This is the dimension along which safeguards and crime control are complements.4. What data identify
Proposition (Non-identification from sanction counts): Suppose regimes $z\in\{0,1\}$ are observed with sanction rates $\sigma_z=p_{C,z}\,c_z+p_{I,z}(1-c_z)$, where $c_z$ is the latent offending share. Then $(p_{C,z},p_{I,z},c_z)$ and the deterrence response $c_1-c_0$ are not identified: for each regime, one equation constrains three unknowns.
Proposition (Validation sample): Suppose a random validation subsample records true culpability $V$ by an independent adjudication assumed error-free. Then $p_{C,z}=\Pr(\text{sanction}\mid V=1,z)$, $p_{I,z}=\Pr(\text{sanction}\mid V=0,z)$ and $c_z=\Pr(V=1\mid z)$ are identified. With random or as-if random $z$, the deterrence effect and $\varepsilon_{p_C}$ along the realised frontier are identified. If adjudication has known misclassification rates, the matrix-inversion correction recovers the same quantities.
Proof: Direct conditioning, and the standard misclassification inversion for a binary latent variable with known error rates. ∎
5. Criminal organisation and open parts
Organised groups internalise $p_I$ only partially: wrongful sanctions on members change the group's labour supply. The offender threshold becomes a group-level participation constraint, and Proposition Proposition (Wrongful sanctions erode deterrence) holds at the group margin. Open: displacement across jurisdictions, where $c$ falls locally and rises elsewhere; distribution-sensitive safeguards, with group-specific $p_I$ caps; and the empirical estimation of $R$, which requires validated case-level data [tsc].Completion Estimate
34%This is a post hoc, heuristic estimate for the full catalogue target. The deterrence-gap calculation and certainty-versus-severity comparison clarify incentive effects, and validation requirements expose nonidentification from sanction counts. Global constrained optimization and policy-specific elasticity identification need stronger assumptions, while organizational adaptation and displacement remain unresolved.
References
- [tsc] S. Tobón, M. M. Sviatschi, N. Cabra-Ruiz, Organised crime, VoxDevLit 17(1) (2025). https://voxdev.org/voxdevlit/organised-crime.
- [png] I. P. L. Png, Optimal subsidies and damages in the presence of judicial error, International Review of Law and Economics 6 (1986), 101--105.
- [becker] G. S. Becker, Crime and punishment: an economic approach, JPE 76 (1968), 169--217.