Why have employer health care costs increased so dramatically over the past few years? The University of California, Irvine conducted the first phase of a study to determine the extent to which various factors, including medical price increases, technology advances, employee and retiree demographics, and changes in employee benefit plans, contributed to the rise in employer costs from 1984-1990, and to estimate the effect of changes in benefit design on employee utilization and expenditures. During phase one, the project expanded an existing database to include premium, expenditure, and utilization data on over 150 insured employed groups and conducted preliminary multivariate analysis of this data.