Measures of patient experience: Should we adjust for case-mix?

Measuring quality of care through the patients’ eyes is important. Patient experience sits at the centre of our efforts to monitor and improve quality; it is one of the core domains of ‘quality’ in health care. But there are some important unresolved methodological issues here. When we measure patient experience, we have a choice about whether to adjust our data for the socio-demographic characteristics of patients. We often call this ‘adjusting for case-mix’. Why might we want to do this? One answer is to create a ‘level playing field’ when comparing data from providers who serve very different patient populations. Without adjusting for patient characteristics, there may problems with fair comparisons, or perceptions of a fair comparison. There are also reasons we might not want to adjust for case-mix. There is a risk that case-mix adjustment could mask poor care provided to some patient groups. Variability in the use of case-mix adjustment reflects both ideological differences and practical uncertainties.

In our work, using UK data on primary care experience from more than 2 million patients, we address some of these uncertainties about the impact of adjusting for case-mix. We found that adjusting for case-mix makes a small, but non-trivial difference because it meaningfully improves performance measurement for practices with less typical and often under-privileged patient populations. We think it is important to discourage practices from ‘cream-skimming’ (avoiding enrolling patients who could be seen as ‘hard to treat’), and to increase perceptions of fairness and engagement in quality improvement activities. Use of case-mix adjustment can help to support these goals.

Want to learn more? See BMJ Quality and Safety here

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