Consumer Assessment of Healthcare Providers and Systems (CAHPS)
Healthcare Cost and Utilization Project (HCUP) FAST STATS
Healthcare Cost and Utilization Project (HCUP) NET
Medical Expenditure Panel Survey (MEPS) Household Component (HC)
Medical Expenditure Panel Survey (MEPS) Insurance Component (IC)
National Healthcare Quality and Disparities Reports (NHQDR)
The following notes describe special methods used in HCUPnet. For more information, refer to HCUPnet Definitions Glossary.
Table of Contents
- Types of hospitals/discharges included in HCUPnet
- Identifying records with ED visits
- Community-Level Statistics
- Clinical Classifications Software Refined (CCSR) and Clinical Classifications Software (CCS)
- Diagnosis Related Groups (DRGs) and Major Diagnostic Categories (MDCs)
- General Conditions
- ICD-10-CM Diagnosis and ICD-10-PCS Procedure Codes
- Conversion of charges to costs
- Aggregate charges and costs
- Rural/urban location of patient’s residence
- Suppressed cases
- Matching your calculations to results from HCUPnet
- Differences between HCUPnet and Fast Stats
- Population-based Rates
Types of hospitals/discharges included in HCUPnet
HCUPnet is based on data from community hospitals in the Healthcare Cost and Utilization Project (HCUP). Community hospitals are defined as short-term, non-federal, general, and other hospitals, excluding hospital units of other institutions (e.g., prisons). HCUP data include OB-GYN, ENT, orthopedic, cancer, pediatric, public, and academic medical hospitals. The data exclude long term care, rehabilitation, psychiatric, and alcoholism and chemical dependency hospitals, although these types of discharges are included if they are from community hospitals.
Identifying records with ED visits
Identification of ED visits with admission to the same hospital was based on the following information:
• A positive charge for emergency department services,
• CPT® codes 99281-99285,
• Revenue codes 450-459, or
• Admission Source or Point of Origin indicating that ED services were received.
HCUPnet provides county- and substate region-level statistical tables and maps for single-year and three-year periods starting in data year 2011 for those States participating in HCUPnet and CLS. Users can obtain population-based information on volume, rates, average length of stay, and hospital costs for inpatient discharges by patient residence county or substate region and by diagnosis or procedure category.
Information can be subdivided further by demographic characteristics such as sex, age group, and payer type. State-level and national benchmarks are presented for comparison.
For further details, see “Methods - Calculating Community-Level Statistics for HCUPnet” PDF.
Clinical Classifications Software Refined (CCSR) and Clinical Classifications Software (CCS)
CCSR for International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM)
- The Clinical Classifications Software Refined (CCSR) for ICD-10-CM diagnoses, used beginning in 2016, aggregates more than 70,000 ICD-10-CM diagnosis codes into over 530 clinically meaningful categories. The categories are organized across 21 body systems, which generally follow the structure of the ICD-10-CM diagnosis chapters:
- Certain Infectious and Parasitic Diseases (INF)
- Neoplasms (NEO)
- Diseases of the Blood and Blood Forming Organs and Certain Disorders Involving the Immune Mechanism (BLD)
- Endocrine, Nutritional and Metabolic Diseases (END)
- Mental, Behavioral and Neurodevelopmental Disorders (MBD)
- Diseases of the Nervous System (NVS)
- Diseases of the Eye and Adnexa (EYE)
- Diseases of the Ear and Mastoid Process (EAR)
- Diseases of the Circulatory System (CIR)
- Diseases of the Respiratory System (RSP)
- Diseases of the Digestive System (DIG)
- Diseases of the Skin and Subcutaneous Tissue (SKN)
- Diseases of the Musculoskeletal System and Connective Tissue (MUS)
- Diseases of the Genitourinary System (GEN)
- Pregnancy, Childbirth and the Puerperium (PRG)
- Certain Conditions Originating in the Perinatal Period (PNL)
- Congenital Malformations, Deformations and Chromosomal Abnormalities (MAL)
- Symptoms, Signs and Abnormal Clinical and Laboratory Findings, Not Elsewhere Classified (SYM)
- Injury, Poisoning and Certain Other Consequences of External Causes (INJ)
- External Causes of Morbidity (EXT)
- Factors Influencing Health Status and Contact with Health Services (FAC)
- Unacceptable principal diagnosis (inpatient data) or first-listed diagnosis (outpatient data) (XXX)
- ICD-10-CM diagnosis codes are not mutually exclusive and individual ICD-10-CM diagnosis codes sometimes document (1) multiple conditions or (2) a condition and a common symptom or manifestation. Assigning only one CCSR category for these codes requires prioritizing the assignment. HCUPnet uses the default CCSR for the principal diagnosis for inpatient data and the default CCSR for the first-listed diagnosis for outpatient data. The all-listed results presented on HCUPnet are based on the non-mutually exclusive, cross-listed CCSR groupings.
- Please visit the CCSR for ICD-10-CM Diagnosis website for more information: https://www.hcup-us.ahrq.gov/toolssoftware/ccsr/ccs_refined.jsp
CCSR for International Classification of Diseases, Tenth Revision, Procedure Coding System (ICD-10-PCS)
- The CCSR for ICD-10-PCS procedures, used beginning in 2016, aggregates more than 80,000 ICD-10-PCS procedure codes into over 320 clinically meaningful categories. The categories are organized across 31 clinical domains. Each ICD-10-PCS code is assigned to a mutually exclusive category. HCUPnet uses the CCSR for the first-listed ICD-10-PCS code when “principal” is selected in the query tool.
- The following abbreviations are used within the category descriptions for the CCSR for ICD-10-PCS
- CABG, Coronary artery bypass graft
- CNS, Central nervous system
- COVID-19, Coronavirus Disease 2019
- EEG, Electroencephalogram
- ENT, Ear, nose, and throat
- ERCP, Endoscopic retrograde cholangiopancreatography
- GI, Gastrointestinal
- ICP, Intracranial pressure
- NEC, Not elsewhere classified
- PCI, Percutaneous coronary intervention
- Rh, Rhesus factor
- Please visit the CCSR for ICD-10-PCS Procedures website for more information: https://www.hcup-us.ahrq.gov/toolssoftware/ccsr/prccsr.jsp
Clinical Classifications Software (CCS) for ICD-9-CM
- The Clinical Classifications Software (CCS) for ICD-9-CM, used prior to 2016, is a diagnosis and procedure categorization scheme that aggregates over 14,000 diagnosis codes and 3,900 procedure codes into a smaller number of clinically meaningful categories. CCS is based on the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM), a uniform and standardized coding system.
- Please visit the CCS for ICD-9-CM Diagnosis and Procedures website for more information: https://www.hcup-us.ahrq.gov/toolssoftware/ccs/ccs.jsp
CCS’s for ICD-9-CM/PCS codes do not map onto CCSR’s for ICD-10-CM/PCS codes; thus, trend analysis across the transition from ICD-9 to ICD-10 is generally not possible.
To improve the user experience and ensure the most relevant and informative data is available to users, HCUPnet limits the set of condition and procedure categories available for query to the most clinically relevant. Further, procedure categories are limited to those that include operating room (OR) procedures based on the HCUP Procedure Classes for ICD-9-CM or Procedure Classes Refined for ICD-10-PCS tools, values 3 and 4 for major diagnostic and therapeutic procedures, respectively.
Diagnosis Related Groups (DRGs) and Major Diagnostic Categories (MDCs)
The Centers for Medicare and Medicaid Services (CMS) defines and uses DRGs as the basis for payment to hospitals. DRGs change annually; a new version is implemented each October 1 by CMS. As a result, DRG information for the last quarter of each year differs from the DRGs in the first three quarters, although in most years this is a minor change. With the introduction of DRG version 25 in October 2007, the DRG system underwent a major change with the addition and redefinition of numerous DRGs. To avoid this shift in DRG information in HCUPnet for 2007 data, DRG version 24 was retained throughout calendar year 2007 and DRG version 25 was applied beginning with calendar year 2008 data.
With the annual changes to the DRGs there are also changes to the DRG labels. The DRG labels prior to version 25 were reviewed and combined to create a label valid across all applicable versions. The same process was used for the labeling of DRGs starting with version 25. Note that the "CC" suffix in the DRG labels refers to "complications and comorbidities;" the "MCC" suffix refers to "major complications and comorbidities."
Since the 4th quarter of 2008, DRGs have required that certain conditions ("healthcare associated conditions" or HACs) have accompanying documentation on whether the conditions were present on admission (POA) or originated during the stay. When POA information for these HACs is missing, cases are assigned to a DRG and MDC indicating "ungroupable," thus information on the specific condition or body system was lost. Because DRG and MDC information is used in HCUPnet to provide insight into what conditions are being treated in hospitals, a version of DRGs and MDCs was created without consideration of whether POA information was available. These DRGs and MDCs begin with 2008 data for the National (Nationwide) Inpatient Sample (NIS), Kids’ Inpatient Database (KID), and State Inpatient Databases (SID).
More information about POA in HCUP SID data is available in the following HCUP Methods Series report: Examination of the Coding of Present-on-Admission Indicators in HCUP State Inpatient Databases (SID).
HCUPnet categorizes adult inpatient discharges into six hospitalization types in the following hierarchical order: maternal, neonatal, mental health/substance use, injury, surgical, and medical. Detailed definitions of these hospitalization types, also known as General Conditions, are below.
Maternal hospitalizations are identified by the Major Diagnostic Category (MDC) 14 Pregnancy, Childbirth and the Puerperium.
Neonatal hospitalizations are identified by MDC 15 Newborns and Neonates with Conditions Originating in the Perinatal Period.
Mental Health/Substance Use is identified by MDC 19 Mental Diseases and Disorders and 20 Alcohol/Drug Use and Alcohol/Drug Induced Organic Mental Disorders.
Injury discharges are identified by a principal diagnosis in the following ranges of ICD-9-CM codes and CCSR principle diagnosis codes based on ICD-10-CM codes:
ICD-9-CM codes (prior to October 1, 2015):
- 800-909.2, 909.4, 909.9: Fractures; dislocations; sprains and strains; intracranial injury; internal injury of thorax, abdomen, and pelvis; open wound of the head, neck, trunk, upper limb, and lower limb; injury to blood vessels; late effects of injury, poisoning, toxic effects, and other external causes, excluding those of complications of surgical and medical care and drugs; medicinal or biological substances.
- 910-994.9: Superficial injury; contusion; crushing injury; effects of foreign body entering through orifice; burns; injury to nerves and spinal cord; traumatic complications and unspecified injuries; poisoning and toxic effects of substances; other and unspecified effects of external causes.
- 995.5-995.59: Child maltreatment syndrome.
- 995.80-995.85: Adult maltreatment, unspecified; adult physical abuse; adult emotional/psychological abuse; adult sexual abuse; adult neglect (nutritional); other adult abuse and neglect.
Exceptions to the above definition of injury are five ICD-9-CM diagnosis codes that are included under two CCS diagnosis categories defining the mental health/substance use hospitalization type:
- CCS = 660 (Alcohol-related disorders): diagnosis 980.0 (toxic effect of ethyl alcohol)
- CCS = 661 (Substance-related disorders): diagnoses 965.00 (poisoning by opium), 965.01 (poisoning by heroin), 965.02 (poisoning by methadone), 965.09 (poisoning by other opiate).
Because of the hierarchical ordering used to assign discharges to hospitalization type, discharges with one of these five principal ICD-9-CM diagnosis codes are assigned to mental health/substance use, not injury.
ICD-10-CM Codes for injuries are identified with the following Clinical Classification Software Refined (CCSR) categories (beginning in 2016):
- INJ001 - Fracture of head and neck, initial encounter
- INJ002 - Fracture of the spine and back, initial encounter
- INJ003 - Fracture of torso, initial encounter
- INJ004 - Fracture of the upper limb, initial encounter
- INJ005 - Fracture of the lower limb (except hip), initial encounter
- INJ006 - Fracture of the neck of the femur (hip), initial encounter
- INJ007 - Dislocations, initial encounter
- INJ008 - Traumatic brain injury (TBI); concussion, initial encounter
- INJ009 - Spinal cord injury (SCI), initial encounter
- INJ010 - Internal organ injury, initial encounter
- INJ011 - Open wounds of head and neck, initial encounter
- INJ012 - Open wounds to limbs, initial encounter
- INJ013 - Open wounds of trunk, initial encounter
- INJ014 - Amputation of a limb, initial encounter
- INJ015 - Amputation of other body parts, initial encounter
- INJ016 - Injury to blood vessels, initial encounter
- INJ017 - Superficial injury; contusion, initial encounter
- INJ018 - Crushing injury, initial encounter
- INJ019 - Burn and corrosion, initial encounter
- INJ020 - Effect of foreign body entering opening, initial encounter
- INJ021 - Effect of other external causes, initial encounter
- INJ022 - Poisoning by drugs, initial encounter
- INJ023 - Toxic effects, initial encounter
- INJ024 - Sprains and strains, initial encounter
- INJ025 - Injury to nerves, muscles and tendons, initial encounter
- INJ026 - Other specified injury
- INJ027 - Other unspecified injury
- INJ032 – Maltreatment/abuse
It should be noted that ICD-9-CM and ICD-10-CM diagnoses codes related to complications of surgical or medical care, or any adverse events or anaphylactic shock resulting from medication, anesthesia, or food are not used in the definition of the injury hospitalization type.
Surgical discharges are identified by a surgical diagnosis-related group (DRG). The DRG grouper first assigns the discharge to a major diagnostic category (MDC) based on the principal diagnosis. For each MDC, there is a list of procedure codes that qualify as operating room procedures. If the discharge involves an operating room procedure, it is assigned to one of the surgical DRGs within the MDC category. Please see the DRG Format.txt program for a listing of the assignments.
Medical discharges are identified as all discharges not classified as any of the above hospitalization types. If the DRG indicates the information on the record is ungroupable (i.e., not identifiable as medical or surgical), the discharge is assumed to be medical. This rarely occurs (less than 0.1 percent of discharges).
ICD-10-CM Diagnosis and ICD-10-PCS Procedure Codes
The option to query individual ICD-10-CM/PCS codes for utilization and outcome statistics has been disabled because the results may not be indicative of the intended clinical/surgical concept. Individual ICD-10-CM diagnoses or ICD-10-PCS procedures often need to be reported in combination to define a clinical/surgical concept, because of the specificity of the individual codes. The ICD-10-CM Coding Guidelines provide a number of examples. Instead, HCUPnet users may query clinical conditions and surgeries by Clinical Classification Software Refined (CCSR), which aggregates ICD-10-CM/PCS into clinically meaningful categories. Additionally, ”Frequencies by Diagnosis and Procedure Codes” (individually and by the CCSR categories) are available in the Documentation section of each nationwide database at the following links:
- National Inpatient Sample (NIS): https://hcup-us.ahrq.gov/db/nation/nis/nisdbdocumentation.jsp
- Nationwide Emergency Department Sample (NEDS): https://www.hcup-us.ahrq.gov/db/nation/neds/nedsdbdocumentation.jsp
- Nationwide Readmissions Database (NRD): https://www.hcup-us.ahrq.gov/db/nation/nrd/nrddbdocumentation.jsp
- Nationwide Ambulatory Surgery Sample (NASS): https://www.hcup-us.ahrq.gov/db/nation/nass/nassdbdocumentation.jsp
Conversion of charges to costs
HCUP databases include information on facility charges, that is, what hospitals bill for services. In order to estimate the costs borne by hospitals to provide services to patients, total charges were converted to costs using cost-to-charge ratios based on hospital accounting reports from the Centers for Medicare and Medicaid Services (CMS). In general, costs are less than charges. For each hospital, a hospital-wide cost-to-charge ratio (CCR) is used because detailed charges are not available in all HCUP States. There is a CCR file for inpatient discharges for use with the National (Nationwide) Inpatient Sample (NIS), Kids’ Inpatient Database (KID), Nationwide Readmission Database (NRD), and State Inpatient Databases (SID), and a CCR file for treat-and-release emergency department visits available for use with the Nationwide Emergency Department Sample (NEDS) and State Emergency Department Databases (SEDD). Please visit the CCR file documentation page for more information: https://www.hcup-us.ahrq.gov/db/ccr/costtocharge.jsp.
There is a time lag in the information used to convert charge data to costs, thus cost data may appear in HCUPnet later than charge data.
Users calculating costs from HCUP databases and the public-use version of the CCR file will notice slight discrepancies with the cost values provided on HCUPnet. The first reason for this difference is that the public use version of the CCR file masks identities of some hospitals by substituting a mean cost-to-charge ratio, while HCUPnet uses unmasked cost-to-charge ratios for all hospitals. The second difference may be because for HCUPnet reporting, inpatient discharges with missing total charges are imputed to be the average total charge for records in the same DRG. For statistics based on the NIS and KID, the DRG averages are calculated within data year. For statistics based on the SID, the DRG averages are calculated within data year and state. The cost-to-charge ratio is applied to the imputed inpatient total charge to determine total cost. Missing total charges for emergency department visits were not imputed.
Costs for stays with a high proportion of ancillary charges (e.g., major surgery) will tend to be overestimated using these cost-to-charge ratios while costs for cases with a high proportion of room and board charges (e.g., tracheostomy, mental illness, premature newborns) will tend to be underestimated.
Aggregate charges and costs
For HCUPnet reporting, inpatient discharges with missing total charges are imputed to be the average total charge for records in the same Diagnosis Related Groups (DRG). The percentage of inpatient discharges missing total charges has decreased over time in the National (Nationwide) Inpatient Sample (NIS), from 7 percent in 2000, to 2 percent in 2010, to 0.5 percent in 2019. For statistics based on the NIS and Kids’ Inpatient Database (KID), the DRG averages are calculated within data year. For statistics based on the SID, the DRG averages are calculated within data year and state. The cost-to-charge ratio is applied to the imputed total charge to determine total cost. Aggregate charges and costs are calculated as the sum of total charges and costs, respectively. Because discharges with missing total charges/costs are imputed, the aggregate will equal the number of discharges times the average total charge/cost.
Aggregate charges and costs for emergency department visits are not reported in HCUPnet.
Information on hospital characteristics is taken from American Hospital Association's Annual Survey. Most of these characteristics are the same as those found in the publicly available versions of the HCUP National (Nationwide) Inpatient Sample (NIS), except for hospital ownership/control. In 1998, the NIS underwent a redesign and the categories of hospital ownership/control were redefined for sampling and reporting purposes. In order to provide continuity of statistics, the pre-1998 definition of hospital ownership/control is used for all years of data and all datasets in HCUPnet.
HCUPnet provides information on 7-day and 30-day hospital readmissions. A 7-day readmission is a subsequent hospital admission in the same or a different hospital within 7 days following an original admission (index stay). A 30-day readmission is a subsequent hospital admission in the same or a different hospital within 30 days following an original admission (index stay). For 30-day readmissions, the discharge date for the index stay must occur between January and November to allow a 30-day follow-up period for all index stays. The 30-day readmission rate is defined as:
the number of stays with at least one subsequent hospital stay within 30 days
the number of hospital stays between January and November
For further details, see "Methods - Calculating Readmissions for HCUPnet" PDF.
"Payer" is the primary expected payer for the hospital stay, based on the first-listed payer. To make coding uniform across all HCUP data sources, Payer combines detailed categories into more general groups:
- Medicare includes fee-for-service and managed care Medicare patients;
- Medicaid includes fee-for-service and managed care Medicaid patients;
- Private insurance includes Blue Cross, commercial carriers, and private HMOs and PPOs;
- Uninsured includes an insurance status of "self-pay" and "no charge;"
- Other includes Worker's Compensation, TRICARE/CHAMPUS, CHAMPVA, Title V, and other government programs.
When more than one payer is listed for a hospital discharge, the first-listed payer is used.
Patients covered by the State Children's Health Insurance Program (CHIP) may be included under Medicaid, private insurance or other insurance, depending on the structure of the state program. Because most state data do not identify CHIP patients specifically, it is not possible to present this information separately in HCUPnet.
Rural/urban location of patient’s residence
For 2003-2006, the rural/urban location of the patient’s residence is a simplified adaptation of the 2003 version of the Urban Influence Codes (UIC), which divide counties into categories based on size and proximity to population centers:
- "Large metropolitan" includes metropolitan areas of 1 million people or more.
- "Small metropolitan" includes metropolitan areas of at least 50,000 but fewer than 1 million people.
- "Non-metropolitan" includes all micropolitan areas (core-based statistical areas of more than 10,000 people but less than 50,000) and all non-urban (rural) areas.
Beginning with 2007, the rural/urban categorization is an adaptation of the 2006 system developed by the National Center for Health Statistics (NCHS) especially for use in healthcare research. The classification emphasizes urban distinctions and is unique in differentiating between central and fringe counties of large metropolitan areas. Smaller metropolitan counties are subdivided by population. Non-metropolitan counties are divided simply into micropolitan and non-core categories.
The NCHS county classifications are based on the Office of Management and Budget (OMB) metropolitan/micropolitan assignments as updated through the 2005 revisions (OMB Bulletin No. 06-01). These assignments were refined using information from the Rural-Urban Continuum Code (RUCC) and Urban Influence Code (UIC) of the Economic Research Service of the U.S. Department of Agriculture and county characteristics from the 2000 Census and 2004 Census Bureau population estimates.
- "Large central" refers to counties of metro areas of 1 million or more population and can be considered cores of large cities.
- "Large fringe" refers to counties of metro areas of 1 million or more population and can be considered suburbs of large cities.
- "Medium and small metro" refers to counties in metro areas with less than 1 million population but with at least 50,000.
- "Micropolitan and noncore" refers to rural counties with less than 50,000 population.
For nationwide data, statistics based on estimates with a relative standard error (standard error / weighted estimate) greater than 0.30 or with standard error = 0 are not reliable. These statistics are suppressed and are designated with an asterisk (*).
The estimates of standard errors in HCUPnet were calculated using SUDAAN software. These estimates may differ slightly if other software packages are used to calculate variances.
Values based on 10 or fewer discharges or fewer than 2 hospitals in the State statistics (SID) are suppressed to protect confidentiality of patients and are designated with an asterisk (*).
Community-Level Statistics in a county or region missing 2% or more of total discharges in the HCUP State Inpatient Database (SID) when compared to the Medicare Hospital Service Area File are suppressed and are designated with an asterisk (*).
Matching your calculations to results from HCUPnet
If you are using HCUPnet to verify your own calculations from the National (Nationwide) Inpatient Sample (NIS), you may notice small discrepancies in some estimates. HCUPnet calculates statistics from SAS datasets. The NIS files available for purchase are ASCII files. Sample weights in the ASCII files are truncated at the fourth decimal place, producing estimates slightly different from those in HCUPnet; however, the differences should be very small. For example, differences in total charges will likely disappear if you round estimates to the nearest $100.
64-bit SAS 9.4 was used to generate the statistics in HCUPNet. Variances estimated by other statistical packages may differ from SAS.
Differences between HCUPnet and Fast Stats
In some cases, slightly different definitions were used to present the information in HCUPnet and Fast Stats. Two specific instances of differences are in the definitions of the maternal and neonatal hospitalization types, and in the version of the CCS software used to classify diagnoses and procedures.
The first source of differences lies in how maternal and neonatal records are defined. For HCUPnet, the definitions of maternal and neonatal use Major Diagnostic Categories (MDCs) to classify diagnosis codes. For Fast Stats, the definitions of maternal and neonatal use MDCs beginning with data year 2016 and rely on the Clinical Classifications Software (CCS) for data years prior to 2016. Compared with using MDCs, the CCS approach assigns approximately 0.9 percent fewer cases to "maternal” because a maternal discharge is classified into a mental health CCS or a substance use CCS when the set of diagnosis codes includes a mental health or substance abuse condition along with a maternal condition (e.g., drug dependence in pregnancy). Similarly, compared with the MDC approach, the CCS approach assigns 0.1 percent fewer cases to “neonatal” because a neonatal discharge is classified into a substance use CCS when the set of diagnosis codes includes a drug effect on the fetus or neonatal drug withdrawal. The CCS approach assigns another 0.1 percent fewer cases to ”neonatal” than the MDC approach because neonatal septicemia is assigned to the septicemia CCS rather than a neonatal CCS.
A second source of differences lies in the timing of analysis. During the redesign of HCUPnet, the most recent version of the CCS software (v2015) was used for all years of diagnosis and procedure statistics prior to 2016. Version 2021.2 of the diagnosis CCSR and version 2021.1 of the procedure CCSR was used for years 2016-2019 statistics. For Fast Stats, the CCS categories are assigned to the National (Nationwide) Inpatient Sample (NIS) based on the most current CCS software. This affects the numbering scheme, counts, and labels for the CCS.
As new data are loaded to HCUPnet, the CCSR software version used will be listed here.
Population-based rates are calculated using national population estimates that correspond to the year of HCUP data. The population estimates are taking from the HCUP Methods Report: "Population Denominator Data for Use with the HCUP Databases," which is available from the HCUP Methods Series.
Population-based rates are only available for categories of patient or hospital characteristics that are in the HCUP Methods Report—for age group, sex, median income of patient's ZIP code, location of patient's residence, region of the U.S., and census division of the U.S. Additionally, in Community-Level Statistics, population rates by patient residence State, substate region, and county are available.
The rate is calculated as number of discharges or visits divided by the population estimate. The standard error of the rate is calculated as the standard error of the number of discharges or visits divided by the population estimate.