Medical practice variations in hospital care; time trends of a spatial phenomenon.

A persistent finding in health services research is that health care delivery and hospital utilisation in the Western world varies widely between areas, both within and between countries. Most studies have concentrated on cross-sectional variations in medical practice. The aim of this article is to investigate whether or not small area variation changed through time. We used hospital discharge rates in the Netherlands for 12 diagnostic or surgical categories to indicate medical practice patterns. The data cover a time span of almost two decades: 1980-1997. First, it was found that in most cases regions are consistently above or below the national trend in the study period. Second, the analysis revealed a statistically significant decline of regional variation in hospital discharges in general during the 1980s and the 1990s. In all but one medical category the results of the separate analyses point towards a downward trend. In one-third of the medical categories this downward trend was statistically significant. Potential parallel changes in regional disparities in need for care, e.g. morbidity or age composition of regional populations or changes in regional differences in care supply are discussed.