Download 1991 NAMCS DATA FILE DOCUMENTATION DESCRIPTION OF

1991 NAMCS DATA FILE DOCUMENTATION
DESCRIPTION OF THE NATIONAL AMBULATORY MEDICAL CARE SURVEY
INTRODUCTION
This data file comprises the data collected by the National
Ambulatory
Medical Care Survey (NAMCS) in 1991, conducted by the National Center
for Health Statistics (NCHS). The National Ambulatory Medical Care
Survey provides data from samples of patient records selected from a
national sample of office-based physicians. These national estimates
describe the utilization of ambulatory medical care services in the
United States. In 1991 there were 33,795 patient records provided by
1,354 doctors that participated in the survey. For a brief
description
of the survey design and data collection procedures, see below. For
a
more detailed description of the survey design, data collection
procedures, and the estimation process see references 1 and 2.
There are two important points relative to analyzing data from this
file
that should be noted:
1-Data 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 13. If more
information is needed the staff of the Ambulatory Care
Statistics
Branch can be consulted by calling 301/436-7132 during regular
working hours.
2-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% or less. 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 the relative standard
error from the information presented in the Appendix. If you
would
like more information, do not hesitate to consult the staff of
the
Ambulatory Care Statistics Branch.
SCOPE OF THE SURVEY
The basic sampling unit for the NAMCS is the physician-patient
encounter
or visit. Only visits in the offices of nonfederally employed
physicians classified by the American Medical Association (AMA) or
the
American Osteopathic Association (AOA) as "office-based, patient
care"
were included in the 1991 NAMCS. In addition, physicians in the
specialties of anesthesiology, pathology, and radiology were excluded
from the physician universe.
- 1 -
Major types of ambulatory encounters not included in the 1991 NAMCS
were
those made by telephone, those made outside of the physician's
office,
and those made in hospital or institutional settings.
SAMPLING FRAME AND SIZE OF SAMPLE
The sampling frame for the 1991 NAMCS was composed of all physicians
contained in the master files maintained by the AMA and AOA as of
December 31, 1990, who met the following criteria:
Office-based, as defined by the AMA and AOA:
Principally engaged in patient care activities;
Nonfederally employed;
Not in specialties of anesthesiology, pathology, and radiology.
The 1991 NAMCS sample included 2,540 physicians: 2,276 MD's and 264
Doctors of Osteopathy. Sample physicians were screened at the time
of
the survey to assure that they met the above-mentioned criteria, 653
physicians did not meet all of the criteria and were, therefore,
ruled
out of scope (ineligible) for the study. The most frequent reasons
for
being out of scope were that the physician was retired, deceased, or
employed in teaching, research, or administration. Of the 1,887 inscope
(eligible) physicians, 72 percent participated in the study. The
physician universe, sample size, and response rates by physician
specialty are shown in table I. Of the participating physicians, 216
saw
no patients during their assigned reporting period because of
vacations,
illness, or other reasons for being temporarily not in practice.
- 2 -
TABLE I.
DISTRIBUTION OF PHYSICIANS IN THE UNIVERSE AND IN THE 1991
NATIONAL AMBULATORY MEDICAL CARE SURVEY SAMPLE BY PHYSICIAN
SPECIALTY AND RESPONSE STATUS: UNITED STATES, 1991.
_________________________________________________________________________
_____
NAMCS
OUT OF
IN
NON-RES-
RES-
RESPONSE
UNIVERSE*
SAMPLE SCOPE
SCOPE
PONSE
PONSE
533
1,354
RATE**
ALL SPECIALTIES
72
334,714
2,540
GENERAL/FAMILY PRACTICE
71
57,754
364
115
249
73
176
OSTEOPATHY
75
14,558
264
58
206
51
155
INTERNAL MEDICINE
63
46,891
206
56
150
56
94
PEDIATRICS
77
28,117
177
65
112
26
86
GENERAL SURGERY
78
19,356
229
62
167
36
131
OBSTETRICS & GYNECOLOGY
72
25,422
171
37
134
38
96
ORTHOPEDIC SURGERY
69
14,237
116
8
108
34
74
CARDIOVASCULAR DISEASES
60
11,027
125
28
97
39
58
DERMATOLOGY
80
6,217
101
16
85
17
68
UROLOGICAL SURGERY
71
7,366
117
18
99
29
70
23,058
105
38
67
14
53
5,758
98
15
83
28
55
13,149
108
23
85
22
63
PSYCHIATRY
79
NEUROLOGY
66
OPHTHALMOLOGY
74
653 1,887
OTOLARYNGOLOGY
68
ALL OTHER SPECIALTIES
73
6,433
105
20
85
27
58
55,371
254
94
160
43
117
_________________________________________________________________________
______
*THESE DATA ARE DERIVED FROM THE AMERICAN MEDICAL ASSOCIATION AND THE
AMERICAN OSTEOPATHIC ASSOCIATION AND REPRESENT THE TOTAL NUMBER OF
PHYSICIANS WHO ARE ELIGIBLE FOR THE NAMCS.
** RESPONSE RATE (PERCENT) = RESPONSE DIVIDED BY IN SCOPE.
- 3 -
SAMPLE DESIGN
The 1991 NAMCS utilized a multistage probability design that involved
probability samples of primary sampling units (PSU's), physician
practices within PSU's, and patient visits within practices. The
first-stage sample included 112 PSU's. A PSU is a county, a group of
adjacent counties, or a standard metropolitan statistical area
(SMSA).
The second stage consisted of a probability sample of practicing
physicians selected from the master files maintained by the American
Medical Association (AMA) and American Osteopathic Association (AOA).
Within each PSU, all eligible physicians were stratified by fifteen
specialty groups: general and family practice, osteopathy, internal
medicine, pediatrics, general surgery, obstetrics and gynecology,
orthopedic surgery, cardiovascular diseases, dermatology, urological
surgery, psychiatry, neurology, ophthalmology, otolaryngology, and
all
other specialties.
The final stage was the selection of patient visits within the
annual practices of sample physicians. This involved two steps.
First,
the total physician sample was divided into 52 random subsamples of
approximately equal size, and each subsample was randomly assigned to
1
of the 52 weeks in the survey year. Second, a systematic random
sample
of visits was selected by the physician during the assigned week.
The
sampling rate varied for this final step from a 100-percent sample
for
very small practices to a 20-percent sample for very large practices
as
determined in a presurvey interview. The method by which the
sampling
rate was determined is described in reference 3.
FIELD ACTIVITIES
The first contact with the sample physician is through a letter from
the
Director, NCHS.
This may be accompanied by a letter from one of the
16
national medical associations that endorse the NAMCS, providing the
physician is a member of one or more of these associations. After
the
physician has received the introductory letter(s) the field
representative telephones the physician to set up an appointment with
him or her to discuss the survey and instruct the doctor on how to
complete the forms.
DATA COLLECTION
The actual data collection for the NAMCS was carried out by the
physician aided by his or her office staff when possible. Two data
collection forms were employed by the physician: The Patient Log and
the Patient Record. The Patient Log is used to sequentially list
patients seen in the physician's office during his assigned reporting
week. This list served as the sampling frame to indicate the visit
for
which data were to be recorded. A perforation between the patient
names
and patient visit characteristics permitted the physician to remove
patient names and protect confidentiality.
- 4 -
Based on the physician's estimate of the expected number of office
visits, each physician was assigned a patient-sampling ratio. These
ratios were designed so that about 30 Patient Records were completed
during the assigned reporting week. Physicians expecting 10 or fewer
visits each day recorded data for all of them, while those expecting
more than 10 visits per day recorded data for every second, third, or
fifth visit based on the predetermined sampling interval. These
procedures minimized the data collection workload and maintained
approximately equal reporting levels among sample physicians
regardless
of practice size. For physicians assigned a patient sampling ratio,
a
random start was provided on the first page of the log, so that
predesignated sample visits on each succeeding page of the log
provided
a systematic random sample of patient visits during the reporting
period.
DATA PROCESSING
In addition to the completeness checks made by the field staff,
clerical
edits were performed upon receipt of the data for central processing.
These procedures proved quite efficient, reducing the item
nonresponse
rates to a negligible amount--5 percent or less for most data items.
For items 5, 9, 13, 15, 16, and 19 on the Patient Record form,
nonresponse rates ranged from 6 to 8 percent.
Information from the Induction Interview and Patient Record forms was
keypunched with 100-percent verification and converted to electronic
data file. Extensive computer consistency and edit checks were also
performed. Data items still unanswered at this point were imputed by
randomly assigning a value from a Patient Record with similar
characteristics; imputations were based on physician specialty and
broad
diagnostic categories.
MEDICAL CODING
The Patient Record form contains four medical items requiring three
separate coding systems. The three coding systems are described
briefly
below. A two-way independent verification procedure was used to
control
the medical coding operation. Differences between coders were
adjudicated by a third coder.
(A)
Patient's Reason for Visit:
Information contained in item
10
(patient's reason for visit) of the Patient Record was coded
according to an updated version of A Reason for Visit
Classification
for Ambulatory Care (RVC) (reference 4). The updated
classification
has not been published as of this writing but the list of codes
is
contained in Appendix II. The classification was updated to
incorporate several new codes as well as changes to existing
codes.
The system continues to utilize a modular structure composed of
seven reason-for-visit modules. The digits 1 through 7 precede
the
RVC codes to identify the various modules, and digits 8 and 9 are
used to identify uncodable entries and blank entries as follows:
- 5 -
Prefix
Module
"1" = symptom module
"2" = disease module
"3" = diagnostic, screening, and preventive module
"4" = treatment module
"5" = injuries and adverse effects module
"6" = test results module
"7" = administrative module
"8" = Uncodable entries
"9" = special code = blank
A maximum of 3 reasons for visit were coded in sequence; coding
instructions concerning the patient's reason for visit are
contained
in the NAMCS Medical Coding Manual (reference 6). Copies are
available upon request.
The SETS version of the NAMCS data allows the user to select
reason
for visit codes at either the 3 digit level or the 4 digit level.
The variable name VISIT3DG should be used to access codes at the
3
digit level; if greater specificity is needed, the variable name
VISITRE will access codes at the 4 digit level.
(B) Physician's Diagnoses: Diagnostic information in item 11 of
the Patient Record was coded according to the International
Classification of Diseases, 9th Revision, Clinical Modification
(ICD-9-CM) (reference 5). For 1991, NAMCS micro-data file
tabulations involving physician's diagnoses, the following
characteristics exist:
1.
The prefix "1" preceding the diagnostic codes has been
added
to identify all codes in the range 001.00-999.90, e.g.
'138100' = '381.00' = Acute nonsupporative otitis media,
unspecified.
2.
The prefix "20" preceding diagnostic codes represents V
code
diagnoses V01.00-V82.90, e.g. '201081' = 'V10.81' =
personal
history of malignant neoplasm of bone.
change
In other words,
the "20" to "V."
NOTE:
The use of prefixes facilitates the calculation of
percent distributions, while substituting "20" for
the
letter "V" allows that all diagnostic fields on the
data file will contain numerical data.
- 6 -
3.
In addition to the diagnostic codes from the ICD-9-CM there
are 3 unique codes in the diagnostic fields that were
developed by the NAMCS staff:
209900 = - noncodable diagnosis
- insufficient information for coding
- illegible diagnosis
209970 =
diagnosis of "none"
900000 =
blank diagnosis
A maximum of three diagnoses were coded in sequence:
coding instructions concerning diagnoses are contained in the
NAMCS Medical Coding Manual (reference 6).
The SETS version of the NAMCS data allows the user to select
ICD-9-CM codes at the 3-digit level. The variable name DIAG3DGT
should be used to access codes at the 3 digit level;if greater
specificity is needed, use the variable name DIAGNOS to access
codes at the highest level.
(C) Ambulatory Surgical Procedures: Information on ambulatory
diagnostic or therapeutic surgical procedures scheduled or
performed
at the current office visit is collected in item 14 of the
Patient
Record form. These data were also coded according to the
International Classification of Diseases (ICD-9-CM), using the
4-digit surgical codes in Volume III. A maximum of two surgical
procedures were coded for each visit.
The SETS version of the NAMCS data allows the user to select
ICD-9-CM codes for ambulatory surgical procedures at the 2-, 3,
and 4-digit level. The variable name AMBSRG1 should be used to
access codes for the first-listed ambulatory surgical procedure
at
the 4-digit level; use the variable SRG12DGT to examine codes
at
the 2-digit level and SRG13DGT for codes at the 3-digit level.
Likewise, to access codes for the second-listed ambulatory
surgical procedure, use variables names AMBSRG2, SRG22DGT, and
SRG23DGT.
(D)
Medication Therapy This Visit:
The NAMCS drug data in item
17
have been classified and coded according to a unique
classification
scheme (reference 7) developed at NCHS. A list of the drug codes
are in Appendix III. The Patient Record form allows for the
recording of up to 5 drugs. The file format includes a
corresponding allocation of drug fields.
- 7 -
A report describing the method and instruments used to collect
and process drug information for the NAMCS has been published
(reference
8). Copies are available upon request.
It should be noted that a substantial amount of information
concerning
each drug is not contained in these data. This additional drug
information will be available in CD-ROM format beginning with the
1992
NAMCS. For years prior to the 1992 NAMCS, the additional drug
information is available as a public-use data tape, or special
tabulations may be requested from the Ambulatory Care Statistics
Branch.
For more information on the availability of the NAMCS drug data,
please
contact the Ambulatory Care Statistics Branch, Division of Health
Care
Statistics, Room 9-52, 6525 Belcrest Road, Hyattsville, Maryland
20782.
The telephone number is 301/436-7132.
HOW TO SELECT PRINCIPAL REASONS, DIAGNOSES, AND MEDICATIONS
The SETS version of the NAMCS allows the user to examine all-listed
occurrences within a single visit for the following variables: Reason
for visit; 3-digit reason; Diagnosis; 3-digit diagnosis; Medications;
by the following variable names: VISITRE; VISIT3DG; DIAGNOS;
DIAG3DGT;
MEDCODE. If the user is interested in principal entries within any of
these variables, then a one in brackets [1] should be added to the
variable name. Hence, the principal diagnosis would be DIAGNOS[1].
The same logic is true for specifying the 2nd or 3rd diagnosis or 4th
or 5th medication listed.
Similarly, when the user is interested in further information about
the
medication codes, then NEWMED with a number in brackets will provide
information on whether the medication is new or continuing (see page
9).
NOTE: The user should be aware of the following conditions when
analyzing records for which there may be multiple occurrences of a
particular code. For example, this situation might occur when the
user is looking at all occurrences of a particular 3-digit diagnosis.
Because up to 3 diagnoses can be coded per record, it is possible
that
a single record may contain multiple occurrences of a diagnosis at
the
3-digit level. An example is a patient who has both an acute (382.00)
and a chronic (382.1) form of otitis media recorded at the office
visit.
When performing a simple query in SETS using unweighted NAMCS data,
the result will reflect all occurrences of the condition of
interest. This means that multiple occurrences of a 3-digit
diagnostic
code appearing on a single record will each be counted in the total
that is output by the SETS program.
However, if the user applies patient weights to the query variable
or otherwise links it to a single-field variable on the record, SETS
will output a count that reflects all RECORDS containing the
condition
of interest. This means that a record that contains more than one
occurrence of a 3-digit diagnostic code will only be counted once.
The same process occurs when the user creates tables in SETS; only
records are counted, not multiple occurrences of a condition on each
record.
- 8 -
As a result, if the user performs a query on, say, DIAG3DGT = 1382,
using weighted NAMCS data, the result may be smaller than what would
be obtained by summing the results of separate queries for
DIAG3DGT[1],
DIAG3DGT[2], and DIAG3DGT[3]. This would apply in cases where there
are multiple occurrences of that 3-digit diagnosis on a single
record.
An additional caveat to users concerns the NEWMED variable. In order
to obtain correct results using this variable, it is necessary to
link it both with a medication code of interest AND with the
appropriate position (whether it is the 1st, 2nd, 3rd, 4th,
or 5th medication listed) on the record.
For example, in order to determine how many times a particular drug
was mentioned as a new medication or as a continued medication, it
is necessary to analyze data for each of the five MEDCODES on the
record individually and then to sum the results. Selecting
a MEDCODE of interest and creating a table for NEWMED without linking
the position of each on the record will produce incorrect results.
In order to do this, the user would first determine the code
for the medication of interest (found in Appendix III), create a
subset for MEDCODE[1] = the code of interest. Then create a table
using the variable name NEWMED[1] to determine how often it was a new
or continued medication. This process would be repeated for the 2nd,
3rd, 4th, and 5th positions of MEDCODE on the record, each time
specifying the corresponding position of NEWMED. The user could then
sum the results to determine how many times the drug was prescribed
as
a new or continued medication.
POPULATION FIGURES
The base population used in computing annual visit rates is presented
in
table II. These figures are based on provisional estimates for the
civilian noninstitutionalized population as of July 1, 1991, provided
by
the U.S. Bureau of the Census. The population estimates are presented
here solely for the purpose of providing denominators for rate
computation and should not be considered as official population
estimates.
IMPORTANT: The SETS program allows the user to obtain visit rates
that
are age-specific, sex-specific, and race-specific. When requesting
visit rates by race, however, the recoded race variable RACER must be
used rather than the original race variable. If visit rates are
requested for NAMCS variables other than age, sex, and race, the SETS
program will calculate them using the total U.S. population as the
denominator. For this reason, users who wish to obtain rates by
geographic region, using regional population estimates as
denominators,
will need to refer to table II and calculate them manually.
The SETS program produces visit rates by age for single years unless
otherwise specifed. To define age groups, use the following syntax
at
the edit prompt in the table option with the age groups of interest:
EXAMPLE:
age (>15, 15 to 24, 25 to 44, 45 to 64, >64)
- 9 -
Table II.
rates
U.S. population 1/ estimates used in computing annual visit
for the National Ambulatory Care Survey, by age, sex, race,
and
geographic region: July 1, 1991.
___________________________________________________________________
|
|
Population Age
|_________________________________________________
Race, Sex,
|
|
|
|
|
and Region
|
All
|
< 5
|
5-14 | 15-24 | 25-34
| Ages
| years | years | years | years
___________________________________________________________________
(in 1,000's 2/)
Total
| 248,712 |
19,379 |
36,249 |
34,534 |
42,404
| 120,724 |
| 127,988 |
9,918 |
9,461 |
18,557 |
17,692 |
17,131 |
17,403 |
20,871
21,533
| 208,202 |
| 101,586 |
| 106,616 |
15,525 |
7,931 |
7,594 |
29,182 |
14,953 |
14,229 |
27,726 |
13,845 |
13,881 |
35,091
17,477
17,614
Sex
Male
Female
Race and Sex
White
Male
Female
Black
Male
Female
|
|
|
30,896 |
14,435 |
16,461 |
3,085 |
1,569 |
1,516 |
5,671 |
2,883 |
2,788 |
5,077 |
2,428 |
2,649 |
5,357
2,430
2,927
Other
Male
Female
|
|
|
9,614 |
4,704 |
4,911 |
770 |
419 |
351 |
1,396 |
721 |
675 |
1,731 |
858 |
873 |
1,957
965
992
Region
Northeast
Midwest
South
West
|
|
|
|
50,300
59,735
84,008
54,670
- 10 -
Table II.
rates
U.S. population 1/ estimates used in computing annual visit
for the National Ambulatory Care Survey, by age, sex, race,
and
geographic region: July 1, 1991--Con.
____________________________________________________________________
|
|
Population Age
Race, Sex,
|__________________________________________________
and Region
| 35-44 | 45-54 | 55-64 | 65-74 | 75 years
| years | years | years | years | and over
____________________________________________________________________
(in 1,000's 2/)
Total
|
38,693 |
26,004 |
21,157 |
18,301 |
11,991
|
|
18,970 |
19,723 |
12,611 |
13,393 |
10,015 |
11,142 |
8,183 |
10,118 |
4,469
7,522
Race and Sex
White
Male
Female
|
|
|
32,854 |
16,333 |
16,521 |
22,261 |
10,913 |
11,348 |
18,367 |
8,729 |
9,638 |
16,323 |
7,348 |
8,975 |
10,874
4,058
6,816
Black
Male
Female
|
|
|
4,283 |
1,916 |
2,367 |
2,707 |
1,198 |
1,509 |
2,155 |
974 |
1,181 |
1,609 |
694 |
915 |
954
344
610
Other
Male
Female
|
|
|
1,556 |
721 |
835 |
1,037 |
500 |
537 |
635 |
312 |
323 |
368 |
141 |
227 |
163
67
96
Sex
Male
Female
Region
Northeast
|
Midwest
|
South
|
West
|
____________________________________________________________________
1/ Civilian noninstitutional population
2/ Numbers may not add to totals because of rounding.
- 11 -
ESTIMATION PROCEDURES
Statistics produced from the 1991 National Ambulatory Medical Care
Survey were derived by a multistage estimating procedure. The
procedure
produces essentially unbiased national estimates and has basically
three
components: (1) inflation by reciprocals of the probabilities of
selection, (2) adjustment for nonresponse, and (3) a ratio adjustment
to
fixed totals. Each of these components is described briefly below.
(1)
INFLATION BY RECIPROCALS OF SAMPLING PROBABILITIES.--
Since
the survey utilized a three-stage sample design, there were
three probabilities: (A) The probability of selecting the
PSU, (B) the probability of selecting a physician within the
PSU, and (C) the probability of selecting a patient visit
within the physician's practice. The last probability was
defined to be the exact number of office visits during the
physician's specified reporting week divided by the number
of
Patient Records completed.
All weekly estimates were
inflated
by a factor of 52 to derive annual estimates.
(2)
ADJUSTMENT FOR NONRESPONSE--Estimates from the NAMCS
data
were adjusted to account for sample physicians who did not
participate in the study. This was done in such a manner as
to
minimize the impact of nonresponse on final estimates by
imputing to nonresponding physicians the practice
characteristics of similar responding physicians. For this
purpose, similar physicians were judged to be physicians
having
the same specialty designation and practicing in the same
PSU.
(3) RATIO-ADJUSTMENT.--A poststratification adjustment was
made within each of fifteen physician specialty groups. The
ratio adjustment is a multiplication factor which had as its
numerator the number of physicians in the universe in each
physician specialty group, and as its denominator the
estimated
number of physicians in that particular specialty group.
The
numerator was based on figures obtained from the AMA-AOA
master
files, and the denominator was based on data from the
sample.
SAMPLING ERRORS
Procedures for calculating sampling errors as well as estimates of
standard errors of statistics derived from the NAMCS are described in
the technical notes of reference 2, as well as Appendix I of this
document.
- 12 -
PATIENT VISIT WEIGHT
The "patient visit weight" is a vital component in the process of
producing national estimates from sample data and its use should be
clearly understood by all data file users. The statistics contained
on
the data file reflect data concerning only a sample of patient
visits--and not a complete count of all the visits that occurred in
the
United States.
Each record on the data file represents one visit in
the
sample of 33,795 visits. In order to obtain national estimates from
the
sample, each record is assigned an inflation factor called the
"patient
visit weight."
By aggregating the "patient visit weights" on the 33,795 sample
records
for 1991 the user can obtain the total of 669,689,374 estimated
visits
made by all patients in the United States.
Marginal tables which may be selected from the main menu present
numbers
of records for selected variables as well as the corresponding
national
estimates of visits obtained by aggregating the "patient visit
weights"
on those records.
PHYSICIAN-PATIENT LINKING CODE
The purpose of this code is to allow for greater analytical depth by
permitting the user to link individual Patient Record forms on the
micro-data file with individual physicians' practices. This linking
code
will enable users to conduct more comprehensive analyses without
violating the confidentiality of patients or physicians. The patient
visit weight should never be applied directly to the physicianpatient
linking code.
- 13 -
REFERENCES 1/
1.
National Center for Health Statistics: National Ambulatory
Medical Care Survey: background and methodology, United
States. National Center for Health Statistics. Vital
Health Stat. 2(61). 1974.
2.
Schappert SM. National Ambulatory Medical Care Survey, 1991
Summary. National Center for Health Statistics. Vital Health
Stat. 13(116.) 1994.
3.
Induction Interview Form. National Ambulatory Medical Care
Survey. Bureau of the Census. OMB NO. 0920-0234.
4.
Schneider D, Appleton L, McLemore T. A Reason for Visit
Classification for Ambulatory Care. National Center for
Health
Statistics.
Vital Health Stat. 2(78). 1979.
5. Public Health Service and Health Care Financing
Administration.
International Classification of Diseases, 9th Revision,
Clinical
Modification (ICD-9-CM). Washington: Public Health Service.
1980.
6.
National Ambulatory Medical Care Survey:
Medical Coding
Manual.
Updated annually.
7.
National Ambulatory Medical Care Survey:
MEDICATION CODE
LIST.
Updated annually.
8.
Koch H, Campbell W. The collection and processing of drug
information. National Ambulatory Medical Care Survey, 1980.
National Center for Health Statistics. Vital Health Stat.
2(90).
1982.
l/Information concerning additional reports using NAMCS data that
have
been published or are scheduled for publication through NCHS may be
obtained from the Ambulatory Care Statistics Branch.
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