Understanding variation in quality improvement: the treatment of sore throats in primary care

In 1988, two practices attempted to improve the prescribing of antibiotics for sore throat. The initiative produced only modest improvements in prescribing practice, a finding the authors found difficult to explain. This paper reanalyses the data from an audit of antibiotic prescribing for sore throat in general practice.

Our aim was to demonstrate the use of Shewhart control charts and to obtain fresh insight into the variations in clinical practice revealed in clinical audit data.

We use Shewhart control charts to explore variation in antibiotic prescribing between GPs and to suggest the action most likely to result in improvement.

Using control charts, it is possible to distinguish two categories of GPs: low prescribers of antibiotics and high prescribers of antibiotics. Low prescribers of antibiotics show common cause variation, indicating that their prescribing is a stable process. Among low prescribers, improvement can best be achieved by changing the common underlying process. One high prescriber of antibiotics is affected by special cause variation. Among high prescribers, improvement can best be achieved by investigating the special causes affecting this GP and learning lessons from the findings.

The original improvement effort took the same action on all GPs in both practices. Our analysis suggests that such an approach was unlikely to be successful and that different actions were needed for high and low prescribers. The control charts provide fresh insights on the original data and guide improvement efforts.