Extrapolation of measures of work for surveyed services to other services

A national survey of physicians produced detailed data on the work involved in performing 372 different services. This article describes methods developed to extrapolate the study data to a larger universe of services, defined by the Physicians' Current Procedural Terminology, edition 4. Because data measuring work inputs for nonsurveyed services presently are unavailable, we devised an extrapolation method that makes use of available charge data without building their inherent distortions into the extrapolated scale. To neutralize the effect of these distortions, we used small, homogeneous families of services as the basic units for the extrapolations and assumed that charges are reasonable indicators of relative work within such families. To produce extrapolated work values within each family, we multiplied an estimate of work based on survey data for a benchmark procedure by charge-based ratios that represent the relationships between surveyed and nonsurveyed services. These extrapolations can be used in constructing a Resource-Based Relative Value Scale.