[Variation in medical practice. Apropos of the use of CAT and NMR in INSALUD]

In this study the variability on the utilization of nuclear magnetic resonance (NMR) and computerized tomography (CT) scan among hospitals and provinces in the INSALUD (Spanish National Health System) is evaluated as well as the role of the availability of resources in the variability.

Data on availability of resources, its use and the reference population for each hospital were obtained from the Specialized Care Information System (SIAE) for the years 1996-1997. The units of analysis were the hospitals and the provinces in the INSALUD territory. The independent variables were the ratio of technologies and professional per inhabitant. Also the waiting list and the economical level of the province were used. Data analysis included the extremal quotient and multiple linear regression.

The ratio of the highest to lowest rate of CT and NMR use is 15 and 27 among hospitals and 3 and 4 among provinces, respectively. The number of neurosurgeons, number of CT apparatus, waiting list for CT and rate of NMR use, all standardized per population, explains 61% of CT variability among hospitals. Among provinces, the number of CT apparatus explains 31% of all variability. For NMR use among hospitals, the number of neurosurgeons, number of orthopedic surgeons and CT use, all variables standardized per population, explains 42% of variability. The amount of equipment is not associated with NMR rate among provinces.

The variation found in the INSALUD territory for the two procedures is high and ecologically associated to the availability of resources. It would be convenient to perform an observational study to confirm the findings and evaluate the possible contribution of inappropriate use to the variation.