Using Concentration Curves to Assess Organization-Specific Relationships between Surgeon Volumes and Outcomes

A well-documented association exists between higher surgeon volumes and better outcomes for many procedures, but surgeons may be reluctant to change practice patterns without objective, credible, and near real-time data on their performance. In addition, published thresholds for procedure volumes may be biased or perceived as arbitrary; typical reports compare surgeons grouped into discrete procedure volume categories, even though the volume-outcomes relationship is likely continuous.

The concentration curves methodology, which has been used to analyze whether health outcomes vary with socioeconomic status, was adapted to explore the association between procedure volume and outcomes as a continuous relationship so that data for all surgeons within a health care organization could be included. Using widely available software and requiring minimal analytic expertise, this approach plots cumulative percentages of two variables of interest against each other and assesses the characteristics of the resulting curve. Organization-specific relationships between surgeon volumes and outcomes were examined for three example types of procedures: uncomplicated hysterectomies, infant circumcisions, and total thyroidectomies. The concentration index was used to assess whether outcomes were equally distributed unrelated to volumes.

For all three procedures, the concentration curve methodology identified associations between surgeon procedure volumes and selected outcomes that were specific to the organization. The concentration indices confirmed the higher prevalence of examined outcomes among low-volume surgeons. The curves supported organizational discussions about surgical quality.

Concentration curves require minimal resources to identify organization- and procedure-specific relationships between surgeon procedure volumes and outcomes and can support quality improvement.