We find that, under a proportional tax deduction system, a nonzero deductible is obtained even though there are no variable costs for the insurer.

• 本文发现当政府对被保险人的净损失提供固定比例税赋抵减时，最适保险契约包含自负额以及共保，且当保险公司的变动成本为零时，最适自负额仍然不为零。