Issues in studying ancillary services

This paper examines several approaches to studying ancillary services usage. The likely generalizability of results provides one criterion for picking site, study population and conditions studied. Breaking up such an aggregate figure as mean annual ancillary services charges per patient into its component parts helps identify the different contributors to high cost practice patterns. Potential differences in case mix are noted as providing the most severe threat to interpreting variation in ancillary services use across practitioners and practice settings. Strategies for dealing with case mix problems include: focusing on specific diseases and specific specialities, stratifying within diagnostic categories, using multiple comparisons and multivariate analysis, pairing of visits and episodes and applying small area techniques.