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Methodology Overview
Our analysts review hundreds of medical journals, trade journals, audits, on-line databases, registries, and market investment reports each month and summarize the data into our Article Reviews. Full source citations are provided for each review. We also compile data from the most recent surveys of the National Center for Health Statistics (NCHS) in our Trend Data reports.

Our analysts go beyond our core sources to constantly monitor larger disease areas and areas in which the data is hard to find. In addition, we are conducting on-going special searches for subscribers that require much broader and more specialized searches.

IPD Sources
Article Review Sources
NHAMCS (National Hospital Ambulatory Medical Care Survey)
NAMCS (National Ambulatory Medical Care Survey)
NHDS (National Hospital Discharge Survey)
CMDT

Journals
The majority of these journals are reviewed on an ongoing basis; the remainder are reviewed periodically.

Acta Neurologica Scandinavica
Acta Oto-Laryngologica
Acta Paediatrica
AIDS American Family Physician
Alimentary Pharmacology and Therapeutics
American Heart Journal
American Journal of Cardiology
American Journal of Clinical Nutrition
American Journal of Emergency Medicine
American Journal of Epidemiology
American Journal of Gastroenterology
American Journal of Health-System Pharmacy
American Journal of Human Genetics
American Journal of Kidney Diseases
American Journal of Managed Care
American Journal of Medicine
American Journal of Obstetrics and Gynecology
American Journal of Ophthalmology
American Journal of Pathology
American Journal of Physical Medicine and Rehabilitation
American Journal of Psychiatry
American Journal of Public Health
American Journal of Respiratory and Critical Care Medicine
American Journal of Roentgenology
American Journal of Surgery
American Journal of Surgical Pathology
American Journal of the Medical Sciences
American Journal of Tropical Medicine and Hygiene
American Optometric Association News
Anesthesia and Analgesia
Anesthesiology
Angiology
Annals of Allergy, Asthma, and Immunology
Annals of Emergency Medicine
Annals of Epidemiology
Annals of General Psychiatry
Annals of Internal Medicine
Annals of Neurology
Annals of Oncology
Annals of Otology, Rhinology, and Laryngology
Annals of Surgery
Annals of the Rheumatic Diseases
Annals of Thoracic Surgery
Antimicrobial Agents and Chemotherapy
Archives of Dermatology
Archives of Disease in Childhood
Archives of Disease in Childhood (Fetal and Neonatal Edition)
Archives of Environmental Health
Archives of General Psychiatry
Archives of Internal Medicine
Archives of Neurology
Archives of Ophthalmology
Archives of Otolaryngology -- Head and Neck Surgery
Archives of Pediatrics and Adolescent Medicine
Archives of Physical Medicine and Rehabilitation
Archives of Surgery
Arthritis and Rheumatism
Arthritis Care and Research
Arthritis Research and Therapy
BJU International
Blood

The National Hospital Ambulatory Medical Care Survey (NHAMCS) is a national probability sample survey of visits to hospital outpatient departments (OPDs) and emergency departments (EDs) conducted by the National Center for Health Statistics (NCHS), Centers for Disease Control and Prevention. The survey is a component of the National Health Care Survey, which measures health care utilization across a variety of health care providers. The national estimates produced from these studies describe the utilization of hospital ambulatory medical care services in the U.S. The 1999 NHAMCS included a national probability sample of visits to the EDs and OPDs of noninstitutional general and short-stay hospitals, exclusive of Federal, military, and Veterans Administration hospitals, located in the 50 states and the District of Columbia. The 1999 NHAMCS included data collected from December 21, 1998 through December 19, 1999, and consisted of a sample of 489 hospitals.

The sampling frame for the 1999 NHAMCS was compiled from the hospitals listed on the April 1991 SMG Hospital Market Data Base. Hospitals with an average length of stay for all patients of less than 30 days (short-stay) or hospitals whose specialty was general (medical or surgical) or children’s general were eligible for the NHAMCS. Excluded were Federal hospitals, hospital units of institutions, and hospitals with less than six beds staffed for patient use. Within each hospital, either all outpatient clinics and emergency service areas (ESAs) or a sample of such units were selected. Clinics were in scope if ambulatory medical care was provided under the supervision of a physician and under the auspices of the hospital. Clinics were required to be “organized” in the sense that services were offered at established locations and schedules. Clinics where only ancillary services were provided or other settings in which physician services were not typically provided were out of scope. In addition, freestanding clinics were out of scope since they are included in the National Ambulatory Medical Care Survey, and ambulatory surgery centers (whether in hospitals or freestanding) were out of scope since they were to be included in the National Survey of Ambulatory Surgery which was first fielded in 1994.

The Bureau of the Census was the data collection agent for the 1999 NHAMCS. Census Headquarters staff were responsible for overseeing the data collection process, training the Census Regional Office staff, and writing the field manual. Regional Office staff were responsible for training the field representatives and monitoring hospital data collection activities. About three months prior to the hospital’s assigned reporting period, NCHS sent a personally signed introductory letter from the Director of NCHS to the hospital administrator or chief executive officer of each sampled hospital. About one week after the mailing of the introductory letter, the Census field representative called the hospital administrator to arrange for an appointment to further explain the study and to verify hospital eligibility for the survey. After the initial visit and the development of the sampling plan, the field representative contacted the hospital coordinator to arrange for induction of the sample ESAs and OPD clinics and for instruction of the hospital staff.

The actual visit sampling and data collection for the NHAMCS was primarily the responsibility of hospital staff. Hospital staff responsible for completing the Patient Record forms were instructed in how to complete each item by the field representatives. Separate instruction booklets for ESAs and OPD clinics were prepared and provided to GUIDe hospital staff in this task. These booklets provided an overview of the survey, sampling instructions, instructions for completing the Patient Record forms, and definitions. The field representative visited the sampled ESAs and clinics each week during the data collection period and maintained telephone contact with the hospital staff involved in the data collection effort.

The standard error is primarily a measure of the sampling variability that occurs by chance because only a sample is surveyed, rather than the entire universe. The relative standard error (RSE) of an estimate is obtained by dividing the standard error of the estimate by the estimate itself and is expressed as a percentage of the estimate. For the ED, the lowest reliable estimate for visits in the ED is 87,000 visits; for the OPD, it is 114,000. (Numbers lower than these have an RSE greater than 30%.) For the 1999 NHAMCS, approximate RSEs for estimated numbers of patient visits to the ED and OPD, respectively, were reported as follows: 10,000 visits, 86.9%, 94.8%; 20,000 visits, 61.6%, 67.5%; 50,000 visits, 39.1%, 43.5%; 100,000 visits, 27.9%, 31.7%; 200,000 visits, 20.1%, 23.8%; 500,000 visits, 13.3%, 17.3%; 1 million visits, 10.1%, 14.5%; 2 million visits, 8.1%, 12.9%; 5 million visits, 6.5%, 11.8%; 10 million visits, 5.9%, 11.4%; 20 million visits, 5.6%, 11.2%; 50 million visits, 5.4%, 11.1%; 100 million visits, 4.3%, 11.1%; 200 million visits, 4.3%, 11.0%.


The target universe of The National Ambulatory Medical Care Survey (NAMCS) includes office visits made in the United States by ambulatory patients to non-Federally employed physicians who are principally engaged in office practice, but not in the specialties of anesthesiology, pathology, or radiology. Sample physicians were asked to complete patient records for a systematic random sample of office visits occurring during a randomly assigned one-week reporting period. During 1994, an estimated 681.5 million office visits were made to non-Federally employed, office-based physicians in the United States (about three visits per person) and in 1993 (762 million office visits). Because the estimates presented in this report are based on a sample rather than on the entire universe of office visits, they are subject to sampling variability. Relative standard errors (all specialties) for 1994 range from 74.8% for 100,000 visits to 3.3% for 50 million visits and above. The smallest reliable estimate for visits to aggregated specialties ranges from 500,000 to 675,000 (551,000 for 1995) visits as a function of survey year. Estimates below this figure have a relative standard error greater than 30 percent and are deemed unreliable by NCHS standards.


The National Hospital Discharge Survey (NHDS), which has been conducted annually since 1965, is a national probability survey designed to meet the need for information on characteristics of inpatients discharged from non-Federal short-stay hospitals in the United States. The NHDS collects data from a sample of approximately 270,000 inpatient records acquired from a national sample of about 500 hospitals. Only hospitals with an average length of stay of fewer than 30 days for all patients, general hospitals, or children’s general hospitals are included in the survey. Federal, military, and Department of Veterans Affairs hospitals, as well as hospital units of institutions (such as prison hospitals), and hospitals with fewer than six beds staffed for patient use, are excluded.

In surveys such as the NHDS, the calculated standard error for small samples can be substantial. For 1995, NHDS estimates less than 5000 generally have a relative standard error of more than 30% or are based on a sample of fewer than 30 cases. For 1995, NHDS estimates of 5000 to 9000 are generally based on fewer than 60 cases with subsequently low reliability. In cases where the error exceeds 30%, the numbers are not provided and, as a result, the sum of component numbers may only approximate the given total. Small sample errors are also pronounced due to the rounding of survey data to the nearest thousand.

In many cases, as with the NHDS, data also tends to understate the "real" patient population. One of the limitations of the NHDS is the trend to perform procedures in an ever-increasing number of free-standing surgical centers and office-based settings. Another limitation is that the NHDS data is only focused on hospital data that does not necessarily reflect the true patient population for diseases such as asthma where patients are seldom admitted to hospitals. To overcome such limitations, TDR continuously compiles entries from various other sources to give users a broader understanding of the topic.


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