ABSTRACT This Material Provides Documentation for Users of the Micro-Data Files of the 2000 National Hospital Ambulatory Medical
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2000 NHAMCS MICRO-DATA FILE DOCUMENTATION PAGE 1 ABSTRACT This material provides documentation for users of the micro-data files of the 2000 National Hospital Ambulatory Medical Care Survey (NHAMCS). The NHAMCS is a national probability sample survey of visits to hospital outpatient and emergency departments, conducted by the National Center for Health Statistics, Centers for Disease Control and Prevention. The survey is a component of the National Health Care Survey, which measures health care utilization across a variety of health care providers. There are two micro-data files produced from the NHAMCS, one for outpatient department records and one for emergency department records. Section I of this documentation, “Description of the National Hospital Ambulatory Medical Care Survey,” includes information on the scope of the survey, the sample, field activities, data collection procedures, medical coding procedures, and population estimates. Section II provides detailed descriptions of the contents of each file’s data record by location. Section III contains marginal data for selected items on each file. The appendixes contain sampling errors, instructions and definitions for completing the Patient Record forms, and lists of codes used in the survey. PAGE 2 2000 NHAMCS MICRO-DATA FILE DOCUMENTATION THIS PAGE HAS BEEN LEFT BLANK INTENTIONALLY. 2000 NHAMCS MICRO-DATA FILE DOCUMENTATION PAGE 3 Table of Contents Page I. Description of the National Hospital Ambulatory Medical Care Survey A. Introduction ..........................................................5 B. Sample design........................................................6 C. Data collection procedures .............................................11 D. Field quality control ..................................................13 E. Confidentiality .......................................................13 F. Data processing......................................................16 G. Medical coding......................................................17 H. Estimation procedures.................................................20 I. Patient visit weight....................................................22 J. Hospital code ........................................................22 K. Clinic type code .....................................................22 L. Population figures ....................................................23 References............................................................26 II. Technical Description of Tape and Record Formats A. Technical description of tape ...........................................28 B. Format of Emergency Department Micro-Data File..........................29 C. Format of Outpatient Department Micro-Data File ..........................56 III. Marginal Data A. Emergency department patient visits .....................................84 B. Emergency department drug mentions....................................86 C. Outpatient department patient visits......................................87 D. Outpatient department drug mentions.....................................90 Appendix I A. Relative standard errors ...............................................92 B. Instructions for completing Patient Record forms ...........................95 C. Definitions of certain terms used in the survey.............................114 Appendix II A. Reason for Visit Classification - summary of codes.........................121 B. Reason for Visit Classification - tabular listing ............................123 Appendix III A. Generic codes and names in numeric order ...............................148 B. Drug entry codes and names in numeric order.............................159 C. National Drug Code directory drug classes ...............................177 User Questionnaire ..........................................................179 PAGE 4 2000 NHAMCS MICRO-DATA FILE DOCUMENTATION Table of Contents (cont.) List of Tables and Figures Table I. Distribution of hospitals in the 2000 National Hospital Ambulatory Medical Care Survey by reporting period and response status ............................8 Table II. U.S. population estimates used in computing annual visit rates for the National Ambulatory Medical Care Survey and the National Hospital Ambulatory Medical Care Survey, by selected characteristics: July 1, 2000 ...................24 Table III. Approximate relative standard errors for estimated numbers of patient visits and drug mentions: National Hospital Ambulatory Medical Care Survey, 2000 ......93 Table IV. Coefficients appropriate for determining approximate relative standard errors of patient visit and drug mention estimates (in 1,000s) by type of estimate and setting: National Hospital Ambulatory Medical Care Survey, 2000 ................94 Figure 1. Emergency Department Patient Record form...............................14 Figure 2. Outpatient Department Patient Record form................................15 2000 NHAMCS MICRO-DATA FILE DOCUMENTATION PAGE 5 I. DESCRIPTION OF THE NATIONAL HOSPITAL AMBULATORY MEDICAL CARE SURVEY A. INTRODUCTION The National Hospital Ambulatory Medical Care Survey (NHAMCS) was initiated to learn more about the ambulatory care rendered in hospital emergency and outpatient departments in the United States. Ambulatory medical care is the predominant method of providing health care services in the United States (1). Since 1973, data on ambulatory patient visits to physicians' offices have been collected through the National Ambulatory Medical Care Survey (NAMCS). However, visits to hospital emergency and outpatient departments, which represent a significant portion of total ambulatory medical care, are not included in the NAMCS (2). Furthermore, hospital ambulatory patients are known to differ from office patients in their demographic characteristics and medical aspects (3). Therefore, the omission of hospital ambulatory care from the ambulatory medical care database leaves a significant gap in coverage and limits the utility of the current NAMCS data. The NHAMCS fills this data gap. The NHAMCS was endorsed by the Emergency Nurses Association and the American College of Emergency Physicians. A complete description of the NHAMCS is contained in the publication entitled, "Plan and Operation of the National Hospital Ambulatory Medical Care Survey" (4). These micro-data files comprise the data collected by the NHAMCS in 2000. The NHAMCS was conducted by the Ambulatory Care Statistics Branch of the National Center for Health Statistics, Centers for Disease Control and Prevention. The NHAMCS provides data from samples of patient records selected from the emergency departments (EDs) and outpatient departments (OPDs) of a national sample of hospitals. The national estimates produced from these studies describe the utilization of hospital ambulatory medical care services in the United States. In 2000, there were 25,622 Patient Record forms provided by EDs and 27,510 Patient Record forms provided by OPDs that participated in the survey. Both data files, ED and OPD, are included in this product. Reports summarizing data from the 2000 NHAMCS are available (5, 6). Please note the following important points concerning analysis of NHAMCS data on this micro- data file: $ PATIENT VISIT WEIGHT Micro-data file users should be fully aware of the importance of the "patient visit weight" and how it must be used. Information about the patient visit weight is presented on page 22. If more information is needed, the staff of the Ambulatory Care Statistics Branch can be consulted by calling (301) 458-4600 during regular working hours. PAGE 6 2000 NHAMCS MICRO-DATA FILE DOCUMENTATION $ RELIABILITY OF ESTIMATES Users should also be aware of the reliability or unreliability of certain estimates, particularly the smaller estimates. The National Center for Health Statistics, which conducts many health surveys, considers an estimate to be reliable if it has a relative standard error of 30 percent or less (i.e., the standard error is no more than 30 percent of the estimate). Therefore, it is important to know the value of the lowest possible estimate in this survey that is considered reliable, so as not to present data in a journal article or paper that may be unreliable. Most data file users can obtain an adequate working knowledge of relative standard errors from the information presented in Appendix I. It should be noted that estimates based on fewer than 30 records are also considered unreliable, regardless of the magnitude of the relative standard error. If you would like more information, do not hesitate to consult the staff of the Ambulatory Care Statistics Branch. B. SAMPLE DESIGN The 2000 NHAMCS included a national probability sample of visits to the emergency and outpatient departments of noninstitutional general and short-stay hospitals, exclusive of Federal, military, and Veterans Administration hospitals, located in the 50 states and the District of Columbia. The NHAMCS was designed to provide estimates based on the following priority of survey objectives: United States; region; emergency and outpatient departments; and type of ownership. The NHAMCS used a four-stage probability design with samples of primary sampling units (PSUs), hospitals within PSUs, clinics within hospitals, and patient visits within clinics. Each stage of sampling is described below. 1. Primary Sampling Units (PSUs) A PSU consists of a county, a group of counties, county equivalents (such as parishes and independent cities), towns, townships, minor civil