ABSTRACT
The concentration of hospital services into bigger units carrying out a higher volume of procedures has been proposed as a means of improving the quality of care. This is based on the assumption that an increase in the volume of activity-at the hospital and/or clinician level-will lead to better clinical outcomes. For example, the American College of Surgeons has recommended that open-heart surgery teams perform at least 150 operations per year so that the necessary skills can be maintained (American College of Surgeons 1984). Similarly, a number of service recommendations of the medical Royal Colleges in England are justified on this basis (Ferguson et al. 1997). Third-party payers and other organisations are increasingly using annual volume thresholds as the basis for credentialing hospitals, units or clinicians (Crawford et al. 1996). In some countries, legislation is used to impose minimum volume thresholds. In the Netherlands, for example, hospitals must obtain a licence to perform open-heart surgery, and the recommended number of procedures is 600 per year (Banta and Bos 1991).
