Comparison of use of outpatient mental health services in an HMO and fee-for-service plans. Sensitivity to definition of a visit.

Whereas previous authors have used a variety of strategies to identify use of mental health services, the sensitivity of estimates to the definition of a visit has been little studied. The authors examined the sensitivity of estimates of use of outpatient mental health services in both HMO and fee-for-service plans to the method of identifying outpatient mental health visits. The HMO and fee-for-service plans had identical benefits (i.e., free care). Data were from the Rand Health Insurance Study. Mental health visits were identified using two definitions: presence of a mental health diagnosis or procedure; and presence of a mental health procedure, diagnosis, or prescription for psychotropic medication in the absence of physical disorders requiring such medications. The major policy conclusions about lower levels of use in the HMO compared to fee-for-service plans were insensitive to the definition of a visit. Nevertheless, estimates of use of general medical providers were higher when psychotropic medications were included in the definition of a mental health visit; this sensitivity to definition was significantly greater for fee-for-service than HMO participants (P less than 0.05). Further, conclusions about the comparability of enrollment mental health status of patients treated by general medical providers in HMO and fee-for-service plans were somewhat sensitive to the definition of a visit.