Understanding the relationship between care hours per patient day and summary hospital-level mortality indicator in English hospitals: A time series approach

Background The Summary Hospital-level Mortality Indicator (SHMI) offers insight into hospital mortality. Prior evidence suggests hospital staffing, particularly of registered nurses (RNs), influences hospital mortality. However, the dynamic relationship between delivered Care Hours Per Patient Day (CHPPD) and SHMI over time remains underexplored. Methods Retrospective analysis of National Health Service (NHS) Trust-level data from December 2020 to May 2024. Care hours data for RNs and other healthcare workers were extracted alongside SHMI values, comprising 302,406 data points from 122 Trusts. Time series including cross-correlation analysis were applied to examine temporal dependencies between CHPPD provided by different staff groups and SHMI. Results There appears to be a relationship between CHPPD and SHMI in English Hospitals. Significant associations were observed between CHPPD and SHMI over time. RNs, median CHPPD was highest in trusts with SHMI below control limits (Median = 5.65), followed by trusts within control limits (Median = 4.87). In trusts with SHMI above control limits, median RN CHPPD was lower (Median = 4.59). For other healthcare workers, median CHPPD in trusts with SHMI above control limits was 3.53, slightly higher than in trusts within control limits (3.51). In trusts with SHMI below control limits, the median CHPPD for other healthcare workers was lowest (3.19). Conclusion This study provides insight into the relationship CHPPD and SHMI across NHS Trusts. Higher RN CHPPD is consistently associated with lower mortality, Trusts with higher-than-expected mortality were asscoaited with lower RN CHPPD.