NAMCS Data Collection and Processing

The U.S. Bureau of the Census acts as the field data collection agent for the NAMCS. The actual data collection for the NAMCS is carried out by the physician aided by his/her office staff when possible, as instructed by Census field representatives. Physicians were instructed to keep a daily listing of all patient visits during the assigned reporting week using an arrival log, optional worksheet, or similar method.  It was to include both scheduled and unscheduled patients but not cancellations or no-shows. Visits were selected from the list using a random start and a predetermined sampling interval based on the physician's estimated visits for the week and the number of days the physician was expected to see patients that week. The sampling procedures were designed so that about 30 Patients Record forms were completed during the assigned reporting week.

Data for sampled visits were recorded on Patient Record forms. At the top of each form, physicians could record the patient's name and record number. However, this information was detached by the physician prior to submitting the completed forms. It was used only to assist physicians in clarifying missing or ambiguous responses that may have been found during the data editing process.

In addition to the completeness checks made by field staff, clerical edits are performed upon receipt of the data for central processing. Detailed editing instructions are provided to manually review the forms and to reclassify or recode ambiguous entries. Computer edits for code ranges and inconsistencies are also performed.

All medical and drug coding and keying operations are performed centrally by Constella Group, Inc. and are subject to quality control procedures. Keying and coding error rates generally range between 0-1 percent for various survey items.

Item nonresponse rates are generally 5 percent or less for NAMCS data items, with some exceptions. These are described in detail in the complete NAMCS downloadable documentation. Imputations for missing data are performed for patient year of birth, sex, race, and time spent with physician. Beginning in 2003, three additional items -- patient ethnicity, have you or anyone in your practice seen patient before, and if so, how many past visits in the last 12 months -- were imputed. Ethnicity and seen before were last imputed in 1996; past visits was not imputed previously.

Drug data are coded using a unique classification scheme developed at NCHS. Listings of drugs by entry name (the name used by the respondent to record the drug on the Patient Record form) and by generic substance are available. The therapeutic class of drugs is based on the National Drug Code Directory.

For users who wish to review a list of patient and drug data items available over multiple years of the survey, refer to the Electronic Data Products web pages.