NIS or NRD: which US inpatient database fits your question

The National Inpatient Sample and the Nationwide Readmissions Database are siblings, but they answer different questions.

Ask NIS about the admission

In-hospital outcomes, complications, costs, and national trends across roughly seven million discharges a year. Each admission is an independent record; once the patient leaves, the data ends.

Ask NRD about what happens next

NRD links admissions of the same patient within a calendar year, which is what you need for thirty-day readmission rates, their predictors, and their costs.

The common trap

Both are survey samples with weights and design variables. Analyse them unweighted and the national estimates, and the reviewer's patience, collapse. Both are also administrative data: coded diagnoses, not charts, so define exposures and outcomes by validated code sets.

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