2017 NHAMCS MICRO-DATA FILE DOCUMENTATION PAGE 1 ABSTRACT This material provides documentation for users of the Emergency Department public use micro-data file of the 2017 National Hospital Ambulatory Medical Care Survey (NHAMCS). NHAMCS is a national probability sample survey of visits to hospital outpatient and emergency departments, and hospital-based ambulatory surgery centers, conducted by the National Center for Health Statistics. The survey is a component of the National Health Care Surveys, which measure health care utilization across a variety of health care providers. NOTE: This document contains complete information on emergency department records only, to accompany the release of the emergency department data file. 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 contains the codebook, which provides detailed descriptions of the contents of the file’s data record by location. Section III contains marginal data for selected items on the file. The appendixes contain sampling errors, instructions and definitions for completing the Patient Record form, and lists of codes used in the survey. PAGE 2 2017 NHAMCS MICRO-DATA FILE DOCUMENTATION SUMMARY OF CHANGES FOR 2017 The 2017 NHAMCS Emergency Department (ED) micro-data file is identical in layout to the 2016 file. The only changes involve some modifications made to help screen text in the survey instrument. These are described in more detail below. Note that the questionnaire changes listed below mainly address items that are included on the public use data file and do not constitute a comprehensive list of all changes to the automated Patient Record form and automated Hospital Induction Interview forms. A. Survey Items 1. New or Modified Items on the Automated Patient Record Form NOTE: The headings and corresponding section locations reflected in the 2017 Emergency Department Patient Record Sample Card may not be identical to those in the automated electronic Patient Record Form. The Sample Card (available at the Ambulatory Health Care Data website) is a general representation of the automated instrument, using a more easily read format that is similar to the original paper forms used in earlier years. Triage: In the diastolic blood pressure item, an additional help text instruction was added: “Palpation (P or PALP) and Doppler (DOPP or DOPPLER) blood pressure techniques can only detect systolic blood pressures. Therefore diastolic blood pressures are recorded as P, PALP, DOPP, or DOPPLER instead of numeric values. Vitals after triage: Under Vitals after discharge, in the diastolic blood pressure item, an additional help text instruction was added: “Palpation (P or PALP) and Doppler (DOPP or DOPPLER) blood pressure techniques can only detect systolic blood pressures. Therefore diastolic blood pressures are recorded as P, PALP, DOPP, or DOPPLER instead of numeric values. Disposition: The category label “Left AMA” was changed to “Left against medical advice (AMA)”. The category label “DOA” was changed to “Dead on arrival (DOA)”. 2. New or Modified Items on the Automated Hospital Induction Interview None. 3. Deleted items None. 2017 NHAMCS MICRO-DATA FILE DOCUMENTATION PAGE 3 B. Data Collection and Comparability of 2017 NHAMCS Estimates with Previous Years of Data Because the 2012 survey year incorporated major changes to the mode of data collection, much research was conducted to assess the comparability of estimates from 2012 with previous years of data. Those results can be found in the 2012 NHAMCS-ED Public Use File Documentation. For 2017, the mode of data collection continued to be the automated laptop-assisted instrument first used in 2012, and additional research was conducted to assess any data anomalies between 2017 and 2016 data. To accomplish this, more than 20 tables of 2017 estimates were compared with the same tables of 2016 estimates. The variables that were compared included most of those published in the annual survey web tables (available from: https://www.cdc.gov/nchs/ahcd/ahcd_products.htm). Significant changes between the two years were noted and investigated. While many estimates were not statistically different in each year, some unexpected results were found. These may reflect actual differences, or they may be related to the changes in item format, the new automated data collection system and/or the increase in Census abstraction. Data users are advised to take these factors into account when using these items or comparing them with previous years. Specific findings include the following, with results being weighted to yield national estimates: ---Significant increases in visits with the following services ordered or provided were noted: blood culture (3.3% to 4.7%); urine culture (8.1% to 10.3%); and influenza test (2.1% to 4.1%). ---Data on ED visits resulting in admission to the observation unit followed by hospitalization (OBSHOS=1) were recently found to have problems relating to internal data processing. These problems have been resolved for 2017, but data for this variable in 2014, 2015, and 2016 are also likely affected, resulting in undercounts. Steps are being taken by survey staff to examine these problems and update the variables as needed. NCHS staff will continue to monitor these and other changes with regard to 2017 data and beyond in an effort to better assess how much may be attributed to data collection and processing vs. real-world treatment patterns. C. Sampling Strata and Variance Estimation Issues NHAMCS currently comprises three components: hospital emergency departments, outpatient departments (OPDs), and ambulatory surgery centers/locations (ASLs). It is important to understand that the first stage of NHAMCS sampling occurs at the geographic level, but the second stage occurs at the hospital level. However, not all hospitals have all three components, and some may choose not to participate in all components, even if they have them. Therefore, it is often the case that not all hospitals participating in NHAMCS are included on the ED file, even though for variance estimation purposes all participating hospitals should be represented (that is, there should be sampling information on the ED public use file for each hospital participating in NHAMCS, in order to obtain the most accurate variance estimation). In years from 1992-2009, when NHAMCS only included two components (emergency departments and outpatient departments), public use data file users were encouraged to combine the ED and OPD public use files for variance estimation purposes. That ensured that even if not all hospitals were represented on the ED file, the inclusion of records from the OPD file resulted in a complete set of participating hospitals and their sampling design variables. Starting in 2010, when the ambulatory surgery (AS) component was added to NHAMCS, analysis was conducted within the Division of Health Care Statistics to ensure that the sampling design information was complete when combining the ED and OPD public use files, even though the AS file was not yet available (the 2010 AS public use file was released in early 2017). Because NCHS has not yet released OPD or AS public use files for 2012 through 2017, internal research is conducted each year to study the effects of only using ED data, without OPD or AS data, using the same methodology employed since 2012. PAGE 4 2017 NHAMCS MICRO-DATA FILE DOCUMENTATION For 20 17 data, internal research was again conducted, using t he same methodology employed since 2012. The effects of the missing sampling design information were less pronounced than in 2016 and should lead t o less variances bei ng understated compared wit h what was found in previous years. For most standard error estimates (approximately 85% of t he 348 estimates tested) the differences were small, but the possible understatement in variances for other estimates means a higher likelihood of a Type I error (finding a significant difference in tahe that dat may not actually exist). In order to decrease the possibility of a Type I error when analyzing the 2017 NHAMCS ED public use file, we recommend that researchers test for significant differences at the alpha=0.01 level, rather than the more commonly used 0.05 level. For questions, please contact the Ambulatory and Hospital Care Statistics Branch (AHCSB) at 301-458-4600 or email [email protected]. 2017 NHAMCS MICRO-DATA FILE DOCUMENTATION PAGE 5 Table of Contents Page Abstract ........................................................................................................................................................1 Summary of Changes for 2017 ....................................................................................................................2 I. Description of the National Hospital Ambulatory Medical Care Survey ..............................................7 A. Introduction ....................................................................................................................................7 B. Sample design ...............................................................................................................................8 C. Data collection procedures ..........................................................................................................10 D. Field quality control ......................................................................................................................11