Why are high performing healthcare organisations so hard to find? In this week's BMJ, Wilson and colleagues report a study that evaluates 69 facilities in 30 US states that receive categorical funding for HIV services.1 The authors assessed performance using a bundle of eight clinical measures considered by a panel of experts to represent high quality of care for HIV. They found that few organisations scored highly across more than a handful of measures.

Interpreting the results at face value suggests that these facilities are not performing well, and that their organisations do not support strong systems of care for people living with HIV. We would expect all clinics to provide comprehensive elements of care that have been shown to improve patients' outcomes. However, closer scrutiny of the study raises methodological and theoretical questions about the selection and measurement of the indicators and, importantly, the association between overall performance and designation as a high performing healthcare organisation.

Composite measures are commonly used to monitor performance in healthcare systems. An overall score is computed by aggregating each component into a bundle of …