Performance of Greek Public Hospitals Before and After the Economic Recession and the Pandemic: Application of a Novel Cost Malmquist Index for Comparing Productivity Across Multiple Groups

<b>Background/Objectives</b>: This study introduces the <i>Multi Group Cost Malmquist Index</i> (CMgm), a novel tool for comparing and ranking the cost efficiency of multiple groups of similar decision-making units operating in different contexts. It was applied to Greek public hospitals to assess productivity change between 2009 and 2021, covering the period before the economic recession and after the second lockdown during the COVID-19 pandemic. The study aimed to determine the impact of these external shocks on hospital efficiency and to identify differences in cost productivity based on hospital size and regional location. <b>Methods</b>: Data envelopment analysis was employed to compute the Malmquist indices for productivity change and ranking. Overall, 109 Greek public hospitals were analysed using three models: as a single group, classified by bed capacity, and classified by regional health authority (RHA). Cost productivity was decomposed into its core measures. <b>Results</b>: During the economic crisis, hospitals improved their cost productivity by 13.2%, whereas during the pandemic, it declined by 32.1%, primarily due to cost frontier deterioration resulting from increased healthcare demand and strained resources. Medium-sized hospitals exhibited higher cost efficiency than small and large hospitals. Regional disparities were also observed, with hospitals in the 5^th and 7^th RHAs outperforming those in 1^st and 2^nd RHAs. <b>Conclusions</b>: The findings highlight the pandemic's disruptive impact on hospital cost productivity compared to the efficiency gains during the economic crisis. It is encouraging, though, that hospitals are recovering again after the lifting of strict lockdown measures. The CMgm is a valuable tool for policymakers, offering insights into hospital performance across multiple groups. Future healthcare policies should prioritise resource optimisation and address regional disparities to enhance system-wide efficiency and resilience in times of crisis.