Fig. 4. Schematic of the federated EHR-based study involving healthcare systems from three countries.

Each site generated three data tables (comma-separated files) containing patient level data: 1) local patient clinical course indicates which days the patient was in the hospital and when the patient died; 2) local patient observation includes first three-character ICD9/10 diagnosis code and laboratory tests, where laboratory test has a numerical value; 3) local patient summary contains demographic variables including age, sex and race. Sites then conduct analysis using these individual level data within their firewall (see Methods).