Both employers' health plans used a variety of requirements and case management procedures to manage care. Since all persons covered by any given plan were subject to the same requirements, one cannot determine from the data used in this study which particular feature had the most influence on service utilization or expenditures. Data from many more plans would be required for such a study. Moreover, in order to determine which plan features have the most influence on service use and costs, such plans would have to share some common features but differ with regard to other important features. In the same vein, without such a rich data source we are unable to determine which specific plan features may be most useful and appropriate for a chronically ill population.
The analyses conducted under the Private Payers Study will show the impact of managed care at an aggregate plan-type level, combining the influence of all of the managed care features of a given plan type under the same 'managed care' rubric. This procedure is typical of the indemnity versus managed care plan comparisons reported in the health services literature.