Session Overview NHDS: Overview Carol DeFrances, Ph.D. Analytic Issues Jean Kozak, Ph.D. Examples of Research Marni Hall, Ph.D. Accessing Data Maria Owings, Ph.D. New Directions Bob Pokras
Overview of the National Hospital Discharge Survey(NHDS) Carol DeFrances, Ph.D.
NHDS Survey Years • Conducted annually 1965-present: • Latest data available: 2002 • 2003 will be available this Winter
NHDS Survey Design • National probability sample: • Short stay non-Federal hospitals • Three stage design: 1. Geographic units 2. Hospital 3. Discharge
More Information on NHDS Design and Operations • NCHS Publications: Series 1, No. 39 “Design and Operation of the National Hospital Discharge Survey: 1988 Redesign” http://www.cdc.gov/nchs/data/series/sr_01/sr01_039.pdf
NHDS Sample Size • Hospitals: • About 500 hospitals sampled per year • Discharges: • Over 300,000 sampled per year
NHDS Data Collection • Manual hospitals - 60% • Automated hospitals - 40%
NHDS Manual Data Collection • NCHS – Statistical Design • Census Bureau – Field Work • Contractor – Coding and Data Entry
NHDS Automated Data Collection • Electronic files obtained from: • States • Commercial firms • Individual hospitals
NHDS Data Processing • NCHS: • Editing • Estimation
NHDS Estimation • Weight: • Inverse of the probability of selection • Adjustments for non-response • Population weighting ratio adjustment
Patient Data • Age • Sex • Race • Expected source of payment • Discharge status • Marital status
Hospital Characteristics • Geographic region • Bed size • Ownership
Medical Data • Diagnoses and procedures • International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM)
Additional Variables • Days of care • Month of discharge • DRG • Weight
New Variables for NHDS Available beginning in the 2001 NHDS: - Source of Admission - Type of Admission
National Survey of Ambulatory Surgery (NSAS) • Survey Years: Annually 1994-1996 • Collected data on ambulatory (outpatient) surgery in the U.S.
NSAS Design • National probability sample • Short stay non-Federal hospitals (418) • Freestanding ambulatory surgery centers (333) • Sample size: • 120,000 sampled visits per year
More Information on NSAS Design and Operations • Survey Design and Operations: NCHS Publications: Series 1, No. 37 “Plan and Operation of the National Survey of Ambulatory Surgery” http://www.cdc.gov/nchs/data/series/sr_01/sr01_037.pdf
Additional Variables Collected for NSAS • Hospital vs. freestanding center • Type of anesthesia • Anesthesia provider
Analytic Issues Lola Jean Kozak, Ph.D.
Topics • Utilization measures • Medical coding system • Statistical issues
NHDS provides data on hospitalizations not people
Measures Include: • Discharges • Days of care • Average length of stay • Diagnoses • Surgeries/procedures
Discharges • Include deaths • Include transfers to other hospitals or long-term care facilities • Do not usually include newborn infants
Days of Care • Total number of days discharged patients spend in the hospital • All stays are counted as at least 1 day. • The admission day is counted, but not the discharge day • The number of days divided by the number of discharges is the average length of stay.
Diagnoses • Disease, injury or other reason for hospitalization • Coded according to US adaptations of the International Classification of Diseases (ICD-9-CM)
Diagnoses • Principal diagnosis: chiefly responsible for hospitalization • First-listed diagnosis: principal if specified, otherwise one listed first
Diagnoses • All-listed: total number of times diagnoses appears on record • Any-listed: discharges with diagnosis in any position on record
Hospital discharges with fractures, 2002 1,609,000 1,387,000 995,000 Principal or first listed Any listed All listed
Surgery/Procedures • Surgical (appendectomy) • Diagnostic (spinal tap) • Therapeutic (chemotherapy) procedures • Coded according to US adaptations of the International Classification of Diseases
NHDS provides data on inpatient procedures not total procedures
Versions of the International Classification of Diseases • 8th revision used 1970-78 • 9th revision used 1979-2004 • 10th revision for use in future
8th Revision • Some codes different than in 9th Revision • Did not use E-codes • Made modifications in coding to accommodate available data
9th Revision • Addenda added annually since 1986 • Codes added, deleted, expanded, and revised • Lists of changes available in annual summary reports, file documentation
Weights • Must use weighted data to obtain unbiased national estimates. • Each record has a weight • Sum the weights of the records
Reliability • To be reliable, estimates must be based on at least 30 records . • And have a relative standard error of less than 30 percent. • Estimates based on 30-59 records should be used with caution.
Standard Errors • Some standard errors are in Advance Data summaries • Generalized error curves are in the Series 13 Annual Summaries and data documentation • Use SUDAAN for specific standard errors - need access to confidential data
Examples of Research Using the National Hospital Discharge Survey Marni Hall, Ph.D.
65 and over 45-64 All ages 15-44 Under 15 Average length of hospital stay by age, 1970-2001
65 and over 45-64 15-44 < 15 1970 1980 1990 2002 Percent distribution of hospital inpatients by age
Hospital Transfers to Long Term Care Facilities in the 1990’s Jean Kozak Long-Term Care Interface – June 2002
2.8 Million 1.6 Million Transfers to long-term care,1990-1999 Number in Millions
12.8 days 8.3 days Average hospital stay for long-term transfers, 1990-1999
Examples ofhealth services research: • Long-stay patients in short-stay hospitalsAcademyHealth Annual Meeting Presentation - Marni Hall and Maria Owings - June, 2003 • Admit source and type NAHDO Annual Meeting Presentation - Maria Owings and Marni Hall - December 2003 • Differences in length of stay in Veterans Health Administration and NHDS hospitalsMedical Care - GE Rosenthal et al. - August 2003
Common NHDS Research Topics: • Deliveries • Type of birth, e.g. cesarean section • Obstetrical procedures • Length of stay
U.S. Trends in Obstetric Procedures, 1990-2000 Jean Kozak and Julie Weeks Birth – September 2002