Development and validation of a frailty index based on data routinely collected across multiple domains in NSW hospitals

Objective(s) To develop and validate a frailty index (FI) that covers multiple domains, using routine hospital data. To investigate the FI's validity, after excluding medication‐related items (FI‐ExMeds), for studies of frailty and polypharmacy. Methods A FI was derived from routine NSW hospital data following standard published guidance. In a development cohort (151 inpatients ≥ 70 years), the FI was correlated with the Reported Edmonton Frail Scale (REFS) using Pearson's R. Validity and distribution of FI and FI‐ExMeds, and correlation with each other, were evaluated in a validation cohort (999 inpatients ≥ 75 years). Results The mean FI for the development cohort was 0.27 (SD 0.09). The FI showed moderate linear correlation with the REFS (n = 148, R = 0.52, P