How much variation in clinical activity is there between general practitioners? A multi-level analysis of decision-making in primary care

Peter Davis,
Barry Gribben,
Roy Lay-Yee,
Alastair Scott

Department of Public Health and General Practice, Christchurch School of Medicine and Health Sciences, University of Otago, Christchurch and Department of General Practice and Primary Health Care, University of Auckland, Auckland, New Zealand;
Department of Public Health and General Practice, Christchurch School of Medicine and Health Sciences, University of Otago, Christchurch and Department of General Practice and Primary Health Care, University of Auckland, Auckland, New Zealand;
Department of Public Health and General Practice, Christchurch School of Medicine and Health Sciences, University of Otago, Christchurch and Department of Community Health, University of Auckland, Auckland, New Zealand;
Department of Public Health and General Practice, Christchurch School of Medicine and Health Sciences, University of Otago, Christchurch and Department of Statistics, University of Auckland, Auckland, New Zealand

Objectives: There is considerable policy interest in medical practice variation (MPV). Although the extent of MPV has been quantified for secondary care, this has not been investigated adequately in general practice. Technical obstacles to such analyses have been presented by the reliance on ecological small area variation (SAV) data, the binary nature of many clinical outcomes in primary care and by diagnostic variability. The study seeks to quantify the extent of variation in clinical activity between general practitioners by addressing these problems.

Methods: A survey of nearly 10 000 encounters drawn from a representativesample of general practitioners in the Waikato region of NewZealand was carried out in the period 1991-1992. Participatingdoctors recorded all details of clinical activity for a sampleof encounters. Measures used in this analysis are the issuingof a prescription, the ordering of a laboratory test or radiologyexamination, and the recommendation of a future follow-up officevisit at a specified date. An innovative statistical techniqueis adopted to assess the allocation of variance for binary outcomeswithin a multi-level analysis of decision-making.

Results: As expected, there was considerable variability betweendoctors in levels of prescribing, ordering of investigationsand requests for follow up. These differences persisted aftercontrolling for case-mix and patient and practitioner attributes.However, analysis of the components of variance suggested thatless than 10% of remaining variability occurred at the practitionerlevel for any of the measures of clinical activity. Furtheranalysis of a single diagnostic group – upper respiratory tractinfection – marginally increased the practitioner contribution.

Conclusions: The amount of variability in clinical activitythat can definitively be linked to the practitioner in primarycare is similar to that recorded in studies of the secondarysector. With primary care doctors increasingly being groupedinto larger professional organisations, we can expect applicationof multi-level techniques to the analysis of clinical activityin primary care at different levels of organisational complexity.

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