2003 NAMCS MICRO-DATA FILE DOCUMENTATION PAGE 1 ABSTRACT This material provides documentation for users of the micro-data file of the 2003 National Ambulatory Medical Care Survey (NAMCS). The NAMCS is a national probability sample survey of visits to office-based physicians conducted by the National Center for Health Statistics, Centers for Disease Control and Prevention. It is a component of the National Health Care Survey which measures health care utilization across a variety of health care providers. Section I, "Description of the National Ambulatory Medical Care Survey," includes information on the scope of the survey, the sample, field activities, data collection procedures, medical coding procedures, population estimates, and sampling errors. Section II provides technical information, including a detailed description of the contents of each data record by location, and a list of physician specialties represented in the survey. Section III contains marginal data and estimates for selected items on the data record. The appendixes contain sampling errors, instructions and definitions for completing the Patient Record form, and lists of codes used in the survey. PAGE 2 2003 NAMCS MICRO-DATA FILE DOCUMENTATION SUMMARY OF CHANGES FOR 2003 The 2003 NAMCS public use micro-data file contains many of the same items as the 2002 file. The items listed below were added or modified for 2003. 1. New/Modified Items a. Was patient’s temperature taken? [TEMPTAKE] – new for 2003. b. Temperature reading (Fahrenheit) [TEMPF] – new for 2003. c. Blood pressure reading (BPSYS, BPDIAS] – new for 2003. d. Diagnostic/screening services – Glucose test [GLUCOSE] is new for 2003. e. Diagnostic/screening services – Glycohemoglobin test [HGBA] is new for 2003. f. Diagnostic/Screening Services – Electrolytes test (ELECTROL] is new for 2003. g. Medications & Injections – increased drug entry fields from six to eight h. Patient ethnicity imputed? [ETHNICFL] - In 2003, missing data for patient ethnicity were imputed for the first time since 1996. A flag was added to identify the imputed records. i. “Have you or anyone in your practice seen this patient before?” imputed? [SENBEFL] – In 2003, missing data for this item were imputed for the first time since 1996. A flag was added to identify the imputed records. j. “If yes, how many past visits in the last 12 months?” imputed? [PASTFL] – In 2003, missing data for this item were imputed. A flag was added to identify the imputed records. Most of these items were added based on suggestions from the expert panel of consultants involved with the NAMCS redesign. Several of them (temperature reading, blood pressure reading, glucose and glycohemoglobin test) have been collected in the emergency department component of the National Hospital Ambulatory Medical Care Survey since 2001. In addition, several items from the Physician Induction Interview, reflecting aspects of the physician's practice, have been added to the NAMCS public use file for the first time in 2003. While data users cannot make physician-level estimates with publicly available data, these items would be especially useful in models as predictors of outcome variables. Also, some of the items could be used to examine differences in visit estimates (for example, looking at visits by disposition status grouped by physicians according to their stated difficulty in making specialty consultation referrals). These new items are: k. Percent of physician’s practice revenue from patient care that comes from Medicare, Medicaid, Private Insurance, and Other [PRMCARER, PRMAIDR, PRPRVTR, PROTHR] (presented as quartiles for each category) l. How many managed care contracts does this practice have? (includes health maintenance organizations, preferred provider organization, independent practice associations, and point-of-service plans) (presented in aggregate categories) [MANCAREC] m. Percent of patient care revenue received by this practice coming from {these) managed care contracts (presented as quartiles) [PRMANR] n. Does your practice use electronic medical records (excluding billing records)? [EMEDREC] o. Does your practice submit claims electronically (electronic billing)? [EBILLREC] p. Are you currently accepting new patients into your practice? [ACEPTNEW] q. From these new patients which of the following types of payment do you accept – Capitated private insurance, non-capitated private insurance, Medicare, Medicaid, Workers compensation, Self-pay, No charge? [CAPITATE, NOCAP, NMEDCARE, NMEDCAID, NWORKCMP, NSELFPAY, NNOCHRGE] r. In the past 12 months, has your practice experienced any difficulty in referring patients with the following types of health insurance for specialty consultation – Medicaid, Medicare, Private Insurance, Uninsured? [REFMDCAD, REFMDCAR, REFPRIV, REFUNINS] 2003 NAMCS MICRO-DATA FILE DOCUMENTATION PAGE 3 Sample Design Variables As first stated in the 2002 NHAMCS public use file documentation, the multi-stage masked sample design variables used for variance estimation in SUDAAN are no longer included on the file. The variables, CSTRATM and CPSUM, which were first included in the 2002 release, take their place, and can be used to estimate variance with SUDAAN’s with-replacement (WR) option, as well as with Stata, SPSS, SAS, and other statistical software packages utilizing an ultimate cluster design for variance estimation. These variables and their use are described more fully in the “Relative Standard Errors” section of the public use file documentation. Drug Characteristics The Ambulatory Care Drug Database underwent substantial revisions in 2002, as described in the 2002 NAMCS Public Use Data File Documentation. For 2003, we continued to add new drugs and update the database as necessary. Because of these revisions to the file, and also because of the addition of a second and third therapeutic class for each drug beginning in 2002, trend analysis with survey data prior to 2002 becomes more problematic. We recommend that researchers download the Drug Characteristics file, which is updated annually, from the Ambulatory Health Care Data website. The characteristics from this file can be applied by matching on drug codes to previous years of data in order to get the most accurate results when doing analysis of drug trends, especially using therapeutic class. We recommend that you use the SAS program (which can be adapted for use with other software) that we have developed and which is downloadable at our website. This program will apply the new characteristics from the most current version of the drug database to previous years of data. Our web address is: http://www.cdc.gov/nchs/about/major/ahcd/ahcd1.htm Reason for Visit Classification The Reason for Visit Classification, developed by NCHS to code the patient’s expressed reason for the medical visit, is updated periodically to reflect reasons for which codes were not previously available and to modify some existing codes to improve the classification scheme. The version of the classification used in a particular survey year is included in that year’s public use documentation. Because of the changes that occur over time, researchers are advised, when doing multi-year analysis involving reason for visit, to check each year’s classification to make sure they are using the best and most complete set of codes for their analysis. Weighting and Estimation Sample data are weighted to produce annual national estimates. Beginning in the 2003 data year, estimates were calculated using a weight that includes a revised adjustment for non- response. In previous years the adjustment accounted for non-response by physician specialty, geographic region, and metropolitan statistical area status. The revised non- response adjustment also accounts for non-response from physicians by practice size, as measured by number of weekly visits, and for variability in number of weeks that participating physicians saw patients during the year. Previously, these characteristics were assumed to be the same for physicians providing patient encounter information and those not providing such information. Research conducted with 2003 data, however, showed that physicians with larger visit volumes were more likely to refuse to participate. In addition, physicians who did not see patients during their assigned week saw patients fewer weeks annually than physicians who did see patients. The revised non-response adjustment uses information collected from physicians during the induction interview. Information on usual weekly visit volume has been collected since 2001 from sample physicians who refuse to provide encounter information. Researchers conducting trend analysis should be aware that estimates based on the revised estimator are expected to be higher in magnitude than estimates using the previous estimator PAGE 4 2003 NAMCS MICRO-DATA FILE DOCUMENTATION when there is greater non-response from physicians with greater volume. NCHS does not plan to release revised estimates for 2001 and 2002 based on the revised estimator. However, more information on the effects of the revised weight relative to the original weight on visit estimates for 2001-2003 will be published in the forthcoming 2003 NAMCS summary report. It is recommended that researchers presenting trend data include a footnote referencing the effects of the revised estimator on their estimates. The following is given as an example: “Beginning in 2003, the National Center for Health Statistics revised the estimator used to produce visit estimates for National