Patterns of care and professional decision making in a New Zealand general practice sample.

It is hypothesised that professional and organisational factors will significantly influence the pattern of care in general practice. This hypothesis is assessed for four key activities: laboratory test orders, prescriptions, referrals, and request for follow up. The data are drawn from a 1% sample of all weekday general practice office encounters in the Hamilton health district recorded over a twelve-month period from February 1979. Overall, 16% of patients receive a laboratory test, under two-thirds a prescription, 8% are referred, and under half receive a specific request for follow up. Interpractitioner variation in activity is substantial for each service: orders for laboratory tests vary between 1% and nearly half of all patients seen, the upper limit of activity for both prescribing and follow up is four patients in five, while rates of referral vary between 0 and 20%. Professional and organisational attributes exert a limited influence on this variation in service activity. Nevertheless, older practitioners, those trained outside New Zealand or without postgraduate qualifications, solo practitioners and practices with high volumes, with low fees and located outside Hamilton, have slightly lower rates of laboratory test orders and slightly higher rates of prescribing. These effects persist after controlling for diagnosis. In a multivariate analysis, diagnostic criteria are seen to be of overwhelming importance in the determination of activity levels. The identity of the practitioner is also a significant influence. Overall, the model accounts for only a fifth of the variation in activity level.