The Choice Among Medical Insurance Plans: Comment
评论了Benjamini和Benjamini（1986）关于健康维护组织与传统保险的理论比较，指出其忽略了需求异质性导致的交叉补贴和福利损失扩大，使结论更模糊。
There are qualifications to the theoretical comparison between Health Maintenance Organizations (HMOs) and conventional insurance (CI), presented in a recent contribution to this Review by Yael Benjamini and Yaov Benjamini (1986). These qualifications make difficult the acceptance, as an unambiguous prediction of economic theory, the authors' conclusions regarding the relative attractiveness of the two methods of insurance to groups of individuals with heterogeneous demands. The authors' arguments are summarized as follows. For homogeneous insureds, an HMO can resemble ideal medical insurance depending on the extent to which the prearranged medical care provided in each health state approximates the desired level for the homogeneous group. Under such conditions, an HMO would be superior to a CI plan in that it is free of the moral that causes a welfare loss under the latter. However, if insureds are heterogeneous in terms of tastes, or any other factor that affects... a welfare loss will also result under the HMO. Because the quantity of medical care provided for a given health state is fixed for an HMO, it cannot satisfy the divergent medical care demands of all insureds in a heterogeneous group. In contrast, the greater flexibility afforded by CI enables insureds with divergent demands to more closely achieve their desired levels of medical care consumption. The welfare loss due to moral hazard is assumed to be little affected by divergent demands, and no other potential effects of demand heterogeneity on the desirability of CI are mentioned. The implication of the authors' analysis is that greater heterogeneity among insureds generally increases preferences for a CI plan over an HMO.' The analysis presented by Benjamini and Benjamini (1986) contains two omissions that pertain to the effect of heterogeneous demand on the desirability of a CI plan. First, heterogeneous demand causes cross-subsidization under a CI plan over and above that due to the incidence of health state. Low demanders subsidize high demanders under CI, whereas, no such cross-subsidization exists under HMOs. This makes ambiguous the effect of heterogeneous demand on general preferences for the two methods of insurance. Second, there appears to be no theoretical basis for assuming that the size of the welfare loss under CI is virtually unaffected by heterogeneous demand. Heterogeneous demand can be shown to increase the welfare loss under a CI plan when this loss is more accurately measured. Thus, the effect of heterogeneous demand, at least in theory, is for this reason much more ambiguous than the Benjamini and Benjamini article implies. The first point is demonstrated with the use of Figure 1. A single, precisely defined unhealthy state, X, and the divergent medical care demands of two representative individuals, A and B, are assumed. A and B are identical in terms of health risk but have differing demands for medical care because of differences in income, tastes, etc. Their respective demands for medical care under a specific CI plan are depicted in Figure 1. Zero administrative costs and a coinsurance rate of .2 are assumed. The price per unit of care is assigned a value of 10 and is equal to marginal cost, which is assumed constant. Under these constraints, individual A de-