Do physician practice styles persist over time? Continuities in patterns of clinical decision-making among general practitioners.

OBJECTIVES: This study seeks to determine whether there are identifiable differences in patterns of clinical decision-making among family physicians, and whether these patterns persist over time.
METHODS: A representative cross-sectional survey of general practice encounters in the Waikato region of New Zealand in 1979-1980 was repeated in 1991-1992. Patterns of clinical decision-making were operationalised as practitioner rates for writing a prescription, ordering a laboratory test or radiological examination and the recommendation of a future follow-up office visit at a specified date. Comparable data were available for a cohort of 50 physicians in both surveys. Multi-level techniques and a simulation exercise were used to study the patterns of decision-making over time.
RESULTS: Raw, unadjusted correlations for the 50 family physicians between the two surveys were 0.24, 0.14 and 0.55 for rates of prescribing, investigations and follow-up, respectively. However, these correlations increased substantially, to 0.55, 0.41 and 0.70, once account was taken of case mix, data clustering and inter-practitioner variation in patient sample size. The extent of this recovery of the underlying correlations was confirmed in a parallel simulation exercise.
CONCLUSIONS: This study confirms the existence of substantial and durable individual practice styles in primary medical care, with implications for the development and successful implementation of clinical guidelines.