The claims-based disability indicators described earlier for some conditions included combinations of diagnosis codes and utilization measures to define potential disability status. However, circularity may be problematic in cross-sectional analyses of utilization or expenditures that compare fee-for-service versus managed care samples if many of those sample members were selected for the study mainly on the basis of utilization criteria. Circularity would be problematic if utilization-based factors drove the plan choice, if subsequent utilization were not controlled well by the plan, and if utilization indicators were used to cast judgments about plan efficiency or outcomes. Inferences about the impact of utilization on plan choice can be made by disaggregating the sample into those identified as potentially disabled solely on the basis of diagnosis and those identified on the basis of diagnosis and utilization criteria. Separate analyses can be conducted for these groups and comparisons across groups can be made to see if the impact of managed care on utilization and expenditures differs for people who were potentially disabled solely because of their diagnoses versus people whose potential disabilities depended upon utilization criteria. In Chapter 6, Chapter 7 and Chapter 8 we study a range of conditions, some identified as potentially disabling on the basis of a diagnosis alone, and others on the basis of both diagnosis and utilization. An alternative approach would be to exclude those whose potential disabilities were defined according to diagnosis and utilization factors (as was done in Chapter 6), but this approach would not have allowed useful comparisons to be made.