Competition and Markets Authority -
Previous hospital mergers have reduced the number of distinct organisations offering publicly funded and provided care in the English National Health Service, reducing choice and between-hospital competition in some areas. This working paper tests the impact of variation in concentration on a new quality indicator: the prevalence of patient harm from falls, pressure ulcers, blood clots and urinary tract infections. It exploits a new source of identifying variation accounting for the multi-product nature of hospitals, using instrumental variables to address endogeneity. It finds that hospital mergers in concentrated areas without offsetting clinical benefits could significantly increase rates of patient harm.