KID_STRATUM is a four-digit stratum identifier used to post-stratify hospitals for the calculation of universe weights.

The hospital's census region, control category, location, teaching status, and bedsize were obtained from the AHA Annual Survey of Hospitals.

• A metropolitan statistical area is considered urban, and a non-metro statistical area is rural.
• Teaching hospitals have an AMA-approved residency program or have membership in the Council of Teaching Hospitals.
• Bedsize assesses the number of short-term acute beds in a hospital.

The hospital's bedsize category is nested within location and teaching status.

Some strata were combined for sampling and weight calculations. Consequently, a given hospital's actual value for a stratifier may differ from those indicated by the value of KID_STRATUM. Each hospital's actual values of stratifiers are contained in separate variables:

Collapse KID_STRATUM for Small Cell Size. If fewer than two frame hospitals, less than 30 uncomplicated births, less than 30 complicated births, and less than 30 non-birth pediatric discharges were contained in a stratum, then the second digit (control) was set to 2 (Private).

Children's Hospitals. KID_STRATUM was set to 9999 (or 9998 in the 2003 KID) for children's hospitals. The AHA Annual Survey of Hospitals and information from the National Association of Children's Hospitals and Related Institutions (NACHRI) were used to identify children's hospitals. AHRQ was consulted about the resolution of any inconsistencies in the coding of hospital type.