Interior optimal imprisonment under diminishing marginal disutility
重新审视了罚款与监禁的最优组合问题，发现当罪犯的监禁边际负效用递减时，最优监禁期限不再是边界解而是内部解，监禁时长成为真正的政策工具。
This note revisits the important question of how fines and imprisonment should be optimally employed. In D’Antoni et al. (2022), a monotone hazard rate condition implies a corner solution for imprisonment in the observable-wealth benchmark when imprisonment disutility is linear. We show that this result is not robust to offenders facing diminishing marginal disutility of imprisonment. The optimal prison term is interior as long as the marginal disutility associated with large imprisonment terms are low and the harms from the offense are large enough to warrant imprisonment. The sentence length thus becomes a genuine policy margin rather than a boundary instrument.