There are significant coding errors in osHPD data on the expected payment source. A non-trivial percentage of patients with pPO (Preferred Provider Organization) coverage is incorrectly coded as in HMOs and vice versa. The prevalence of these errors has increased as a result of osHPD`s introduction of a new source of payment expected for P3s. Measurement problems are particularly important in elderly patients. Many patients over the age of 65, who are still covered by a commercial insurance plan, are wrongly coded as Medicare policyholders. With the fact that during the period we analyzed, Medicare participants and recipients are grouped into a single payment category in the Fee-for-Service (FFS) program, which means that OSHPD data essentially provide no information on insurance coverage for elderly patients. The lack of information on HMO coverage for Medicare recipients is regrettable given the high percentage of Senior California included in the plans and the importance of research questions related to the impact of this coverage. The revision of the definitions of variables adopted in 1999 is expected to significantly improve this situation. Under current guidelines, the expected source of payment is covered by two variables, the first of which is the payer category (nine categories including the private, Medicaid and Medicare) and the second, which relates to the type of payer (four categories, including HOV, other managed care and traditional care). This change represents a potentially significant improvement in the data.
Assuming that coding is correct, it should now be possible to use occupational health and safety offloading data to compare the results for Medicare receptors in HMOs with those in the service fee industry. Of course, in light of the results of this study, accuracy should not be taken for granted. 4 In Spetz`s (1999) analysis, the average of these variables is used at the district level to measure the penetration of HOV at the market level. Capps et al. (2001) report the average value of a patient variable called HMO/PPO. However, as they use the 1991 OSHPD data, we assume that this variable is identical to the HMO indicator variable we use here. We conclude that the 1990s occupational health and safety redundancy data provide little or no useful information on insurance coverage for patients over 65. Part of this amount is a direct result of OSHPD`s coding guidelines, which, during the period of our analysis, requested that all Medicare recipients in the FFS program and those enrolled in HMS be grouped into a single expected source of payment.7 In addition, we find that a large proportion of patients over the age of 65 but covered by a commercial plan are wrongly coded as Medicare coverage.