On the correlation between outcome indicators and the structure and process indicators used to proxy them in public health care reporting

Hospital quality indicators provide valuable insights for quality improvement, empower patients to choose providers, and have become a cornerstone of value-based payment. As outcome indicators are cumbersome and expensive to measure, many health systems have relied on proxy indicators, such as structure and process indicators. In this paper, we assess the extent to which publicly reported structure and process indicators are correlated with outcome indicators, to determine if these provide useful signals to inform the public about the outcomes. Quality indicators for three conditions (breast and colorectal cancer, and hip replacement surgery) for Dutch hospitals (2011-2018) were collected. Structure and process indicators were compared to condition-specific outcome indicators and in-hospital mortality ratios in a between-hospital comparison (cross-sectional and between-effects models) and in within-hospital comparison (fixed-effects models). Systematic association could not be observed for any of the models. Both positive and negative signs were observed where negative associations were to be expected. Despite sufficient statistical power, the share of significant correlations was small [mean share: 13.2% (cross-sectional); 26.3% (between-effects); 13.2% (fixed-effects)]. These findings persisted in stratified analyses by type of hospital and in models using a multivariate approach. We conclude that, in the context of compulsory public reporting, structure and process indicators are not correlated with outcome indicators, neither in between-hospital comparisons nor in within-hospital comparisons. While structure and process indicators remain valuable for internal quality improvement, they are unsuitable as signals for informing the public about hospital differences in health outcomes.