Hospitals in Germany have been required to have an internal quality management system (QMS) since 2000. Although formal certification of such systems is voluntary, the number of certifications has increased steadily. The most common standards in Germany are ISO 9001, which is also widely used internationally, and KTQ (Kooperation für Transparenz und Qualität im Gesundheitswesen), which was developed specifically for the German health care sector. While a large body of literature has investigated the impact of QMS certification on performance in many industries, there is only scarce evidence on the causal link between QMS certification and technical efficiency. In the present study, we seek to elucidate this relationship using administrative data from all German hospitals from 2000 through 2010 combined with information on certification. Our analysis has three steps: First, we calculated efficiency scores for each hospital using a bootstrapped data envelopment analysis. Second, we used genetic matching to ensure that any differences observed could be attributed to certification and were not due to differences in sample characteristics between the intervention and control groups. Third, we employed a difference-in-difference specification within a truncated regression to examine whether certification had an impact on hospital efficiency. To shed light on a potential time lag between certification and efficiency gains, we used various periods for comparison. Our results indicate that hospital efficiency was negatively related to ISO 9001 certification and positively related to KTQ certification. Moreover, coefficients were always larger in the period between first certification and recertification. 
Changes in technical efficiency after quality management certification: A DEA approach using difference-in-difference estimation with genetic matching in the hospital industry