“…We also constructed other risk‐adjustment variables from the PROM survey, namely, the duration of problems, and whether the patient lives alone, considered herself disabled, or required help filling in the questionnaire. In the length of stay model, we controlled for the healthcare resource group (HRG, the English equivalent of Diagnosis‐Related Groups) to which the patient was allocated and which form the basis of the prospective payment system used to reimburse English hospitals (Grašič, Mason, & Street, ).…”