Abstract
BackgroundThe hospital standardized mortality ratio (HSMR) is developed to evaluate and improve hospital quality. Different methods can be used to standardize the hospital mortality ratio. Our aim was to assess the validity and applicability of directly and indirectly standardized hospital mortality ratios.MethodsRetrospective scenario analysis using routinely collected hospital data to compare deaths predicted by the indirectly standardized case-mix adjustment method with observed deaths. Discharges from Dutch hospitals in the period 2003–2009 were used to estimate the underlying prediction models. We analysed variation in indirectly standardized hospital mortality ratios (HSMRs) when changing the case-mix distributions using different scenarios. Sixty-one Dutch hospitals were included in our scenario analysis.ResultsA numerical example showed that when interaction between hospital and case-mix is present and case-mix differs between hospitals, indirectly standardized HSMRs vary between hospitals providing the same quality of care. In empirical data analysis, the differences between directly and indirectly standardized HSMRs for individual hospitals were limited.ConclusionDirect standardization is not affected by the presence of interaction between hospital and case-mix and is therefore theoretically preferable over indirect standardization. Since direct standardization is practically impossible when multiple predictors are included in the case-mix adjustment model, indirect standardization is the only available method to compute the HSMR. Before interpreting such indirectly standardized HSMRs the case-mix distributions of individual hospitals and the presence of interactions between hospital and case-mix should be assessed.
Highlights
In the last decades increasing attention is directed towards the quality of care of hospitals
The hospital standardized mortality ratio (HSMR) has been debated for various reasons: the credibility of the link between quality of care and risk adjusted mortality [8,9,10], the variables that are used for case-mix adjustment [11], and issues regarding coding of these variables [12]
Ethics Statement To study the impact of this phenomenon caused by indirect standardization on real clinical data, we have conducted a series of analyses on the Dutch HSMR figures, permitted by the Dutch Hospitals Association and the Dutch University Medical Centers Association
Summary
In the last decades increasing attention is directed towards the quality of care of hospitals. Various performance indicators have been developed to express quality of care, among which the hospital standardized mortality ratio (HSMR). Developed and implemented in 1999, the HSMR is used as a key hospital quality indicator in various countries including the United Kingdom, the United States, Canada, and the Netherlands [2,3,4,5,6,7]. The HSMR has been debated for various reasons: the credibility of the link between quality of care and risk adjusted mortality [8,9,10], the variables that are used for case-mix adjustment [11], and issues regarding coding of these variables [12]. The hospital standardized mortality ratio (HSMR) is developed to evaluate and improve hospital quality. Our aim was to assess the validity and applicability of directly and indirectly standardized hospital mortality ratios
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