Frequently
Asked Questions (FAQ’s)
Q: What do the
letters in NAMCS and NHAMCS stand for?
A: National Ambulatory Medical Care Survey; National Hospital Ambulatory
Medical Care Survey.
Q: What is the
difference between NAMCS and NHAMCS?
A: The NAMCS samples visits to physician offices. The NHAMCS samples
visits to hospitals (outpatient
departments and emergency departments).
Q: Why is the NHAMCS
sometimes referred to as two surveys?
A: The NHAMCS is made up of two components: hospital outpatient
departments (OPD) and hospital
emergency departments (ED).
Q. How are the data
used?
A. NAMCS and NHAMCS data are used to statistically describe the patients
that utilize physician services and hospital outpatient and emergency
department services, the conditions most often treated, and the diagnostic
and therapeutic services rendered, including medications prescribed. The
data are used by public health policy makers, health services researchers,
medical schools, physician associations, epidemiologists, and the print
and broadcast media to describe and understand the changes that occur in
medical care requirements and practices. The data are disseminated in the
form of public health reports, journal articles, and microdata files.
Q: Can the
ambulatory medical care surveys be used to find out how many people have a
certain diagnosis?
A: No. The ambulatory medical care surveys (NAMCS and NHAMCS) are not
based on a sample
of the population. They are based on a sample of visits rather than a
sample of people. The
data can be used to find out how many ambulatory care visits were made
involving a certain
diagnosis. To get an idea of utilization of ambulatory care in the
population, the number of visits
can be divided by the population of interest to get a rate of visits for a
diagnosis of interest.
Q: Must one always
use a single year or care setting when analyzing the ambulatory medical
care data?
A. No. Survey years with the same patient record form (survey instrument)
can be easily combined. Years
where the same question of interest is asked can be combined. Within
years, the three care settings can be combined because they have different
sampling frames.
Q: Is it possible to
obtain State-level estimates from the NAMCS and NHAMCS data?
A. The surveys are primarily designed to provide national estimates.
Geographic region (Northeast, Midwest, South, and West) and metropolitan
statistical area status (a yes/no field indicating whether the visit took
place in an urban or rural area) are the only geographic designations on
the files. The first stage of sampling is the selection of a group of PSUs
(primary sampling units). These are geographic segments composed of
counties, groups of counties, towns and townships or minor civil
divisions, or metropolitan statistical areas. They may cross State lines
and will not necessarily be selected in every State. In fact, the surveys
are not designed to sample ambulatory care visits in every State, and
meaningful estimates cannot be made on a State-level basis.
Q. How can variances
be calculated for NAMCS and NHAMCS estimates?
A. Prior to
calendar year 2002, NAMCS and NHAMCS public use files did not contain the
sample design variables that are needed by sophisticated computer software
like SUDAAN, which computes standard errors while taking the complex
multi-stage sampling design into account. The design variables are
confidential and have never been released to the general public. However,
in 2002, a 5-year research project culminated in a plan to mask sample
design variables so that they could be released without fear of disclosure
of survey participants. The 2000 public use files were released with these
variables, and files from 1993-1999 were re-released to include them. We
are currently working to add masked sample design variables to NAMCS files
from 1989-1992, and to NHAMCS files. Please see the survey
documentation for more information about using computer software like SUDAAN to calculate standard errors.
Another method for calculating
variances for NAMCS and NHAMCS estimates which does not require using
SUDAAN or similar software is to use a generalized variance curve
as described in the public-use file documentation. Use
of this curve will produce approximate standard errors for estimates of
visits and drug mentions. The variances that are produced in this way,
using methods explained in the survey documentation, will, in general, be
less precise compared with those produced using SUDAAN.
Users with additional data needs
may contact the NCHS Research Data Center to conduct on-site research with
restricted survey files. More
information about the Research
Data Center is available on the NCHS
website.
Q. Under what
authorization does NCHS collect this information?
A. The NAMCS and NHAMCS fall under Title 42, United States Code, Section
242K, which permits data collection for health research. The
confidentiality of the data is protected by Title 42, United States Code,
Section 242m(d). Information collected in the surveys is used only for
statistical purposes. No information that could identify a person or
establishment can be released to anyone - including the President,
Congress, or any court, without the consent of the provider. The Census
Bureau staff, who are collecting the data for NCHS, sign an affidavit
making them subject to the Privacy Act, the Public Health Service Act and
other laws that require the data be protected. The NCHS and Census Bureau
maintain a perfect record in protecting the privacy of health care
providers and patients.
Q. How does the
HIPAA Privacy Rule affect a physician’s or hospital’s decision to
participate?
A. The final Privacy Rule has been published as required by the Health
Insurance Portability and Accountability Act of 1996 (HIPAA). Health
care providers who transmit financial and administrative health
information electronically must comply with the Rule as of April 14, 2003.
The Privacy Rule permits physicians and hospitals to make
disclosures of protected health information without patient authorization
for public health purposes or for research that has been approved by an
Institutional Review Board with a waiver of patient authorization.
The
NAMCS and NHAMCS meet both of these criteria.
Additionally, disclosures may be made under a data use agreement
with NCHS.
Q. Why does patient’s
name appear on the form if NCHS does not collect it?
A. We ask that the survey respondent keep that part of the form above the
perforation, which does contain the patient’s name. We collect the
remaining information. We want the respondent to keep the patient’s name
so that if we need to contact him or her regarding missing or conflicting
information from the abstract form, then we can give the physician or
hospital staff our unique ID number, which is also contained on the top
portion of the form that is retained. This will allow the survey
particpant to locate the patient’s medical record without disclosing the
name to us.
Q. Will anyone be
able to identify a health care provider in the survey data?
A. No, we are legally bound to assure the confidentiality of all responses
including anything that might result in a physician’s practice or
hospital being identified. The data files that are released for research
do not include any provider or patient identifying information.
Q. Is participation
mandatory?
A. No, participation is completely voluntary.
Q. Then why should
physicians and hospitals participate?
A. NAMCS participation is important because without one physician’s
participation, neither that physician nor others similar to that physician
are represented in the national description of office-based patient care.
Physicians are randomly chosen to represent not only themselves, but
thousands of other physicians in the same geographic region and medical
specialty. The same justification applies to the hospitals that
participate in the NHAMCS.
For specific questions
about how NCHS protects the information physicians and hospitals provide,
contact:
Alvan
O. Zarate, Ph.D.
Confidentiality Officer, NCHS
3311 Toledo Road, Room 7116
Hyattsville, MD 20782
Telephone: (301) 458-4601
Email: AZarate@cdc.gov
This page last reviewed
January 11, 2007
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