The United States is unique in having several national health surveys. Other countries have good surveys, but for the most part they are not national and one must assume that, for example, the southeast part of a country is like the northwest. Because the United States has national surveys, we know whether the southeast is, or is not, like the northwest. That provides us a great advantage in formulating policy for a country as large and diverse as the United States. For this article, four national surveys and one state-based survey have been selected to illustrate the kinds of impact each can have. The basis for this choice was that each of the surveys has a unique design feature that makes its impact different from the others, each is household based, each covers the total noninstitutionalized population, and each is old enough to have had a demonstrable impact.
NATIONAL HEALTH INTERVIEW SURVEY
The oldest of the population-based surveys is the National Health Interview Survey (NHIS), conducted by the National Center for Health Statistics (NCHS) at the Centers for Disease Control and Prevention (CDC). The National Health Survey Act was signed into law by President Eisenhower on July 4, 1956; and the NHIS went into the field precisely one year later. It's unique design feature is that it is a continuing survey, with each weeks' sample capable of producing national estimates. This design immediately proved its worth. When the flu epidemic hit in the fall of 1957, the NHIS was able to produce weekly estimates of the number of incident cases—the first time immediate data on cases, not deaths, were available. A few years later, the NHIS data were critical in formulating the new Medicare and Medicaid programs. Estimates of the conditions of the people covered and the costs of those programs were still not precise, but they were far better than they would have been without the NHIS.
The original intent of the NHIS was to estimate the incidence of acute conditions, the prevalence of chronic ones, and the use of medical care. Over time, supplemental questionnaires were added to the base questionnaire and some of those supplements have contributed the main impact of the NHIS. The Child Health Supplements, the Supplement on Aging, the Supplement on Disability, and the Cancer Supplements have all been used by their sponsoring agencies to monitor their missions and implement new programs.
By the late 1970s, the CDC had shifted its focus to the prevention, rather than the cure, of disease. In 1979, Healthy People: The Surgeon General's Report on Health Promotion and Disease Prevention appeared. This was followed, in 1980, by another report, Promoting Health/Preventing Disease: Objectives for the Nation. That report outlined 226 health goals (Healthy People 2010 contains 467 goals). Progress toward these goals was to be assessed by data. Most of the data, especially in that first decade, came from the NHIS. Even in Healthy People 2010, the NHIS provided data for more goals (73) than any other data source. Again the unique survey design of the NHIS served well; it was the only survey that was repeated every year and that had a core of unchanging questions that could be used to monitor change.
A second design feature of the NHIS is that while the base questionnaire changes relatively little, there are supplemental modules that enable the survey to be used to answer immediate and important policy questions. Some of these modules have also been used as the basis for longitudinal studies such as the Longitudinal Study of Aging.
NATIONAL HEALTH AND NUTRITION EXAMINATION SURVEY
Even when the NHIS was first in the field, its designers knew that respondents can report only what they know and what they are willing to report, and that there was a need for data based on objective standardized physical examinations. Yet the only physical data on the health of the American people came from the draft examinations, which were far from standardized. Therefore, the National Health and Nutrition Examination Survey (NHANES) was created with the unique feature that mobile examination centers were moved around the country so that the examinations and their environments were constant; the only thing allowed to vary was the people being examined. NHANES has had an impact on both policy and practice. The growth charts (which have recently been modified) have influenced well-baby care all over the world. Charting blood-lead levels over time and across population groups resulted in Environmental Protection Agency changing the schedule for removing lead from gasoline from a gradual phaseout to removing the lead at once. The standardized measures over time have enabled the National Heart Lung and Blood Institute to monitor the levels of blood pressure and cholesterol in the United States population. The availability of "normal" measures of many elements of human physiology have revised the textbook standards that, before NHANES, were dependent on such populations as twenty prisoners in a state prison.
During their early years, these two surveys were conducted by the U.S. Bureau of the Census (the NHIS still is), which was reluctant to ask sensitive questions because of the possible impact on the decennial census. Yet the need for data on the so-called sensitive topics was increasing and had to be met.
NATIONAL HOUSEHOLD STUDY ON DRUG ABUSE
In 1971 and 1972, the National Commission on Marijuana and Drug Abuse sponsored the first two studies of what is now the National Household Survey on Drug Abuse (NHSDA) sponsored by the Substance Abuse and Mental Health Services Administration. The NHSDA added two unique features. First, it was, and is, a completely anonymous survey. Second, adolescents were both oversampled and responded for themselves. Recently, it has added another feature; it is the only nationally administered survey designed to produce estimates for each state. Like the NHIS, it is a repeated cross-sectional survey, making it very useful in tracking short-term changes. In addition to informing policy, the NHSDA has changed policy. The NHSDA data showing that most users of illicit drugs are employed led to many workplace initiatives such as Executive Order 12564, that established a drug-free federal workplace in 1986. The substantial increase in use of illicit drugs by youths in the early 1990s along with data showing the relationship between marijuana use and use of harder drugs led to a major emphasis on preventive activities.
MEDICAL EXPENDITURE PANEL SURVEY
One of the interesting aspects of the legislation enabling the NHIS was that it encouraged research in survey methods. Partly because of that research it became increasingly obvious that respondents did not recall all of the medical care they or their families had received in the past year. A better method was needed to provide good estimates of the costs of medical care. For that reason a new survey was born in 1977 at the University of Chicago, a survey that is now the Medical Expenditure Panel Study (MEPS) sponsored by the Agency for Healthcare Research and Quality. The MEPS added two new dimensions to the basic household survey. The first was that instead of asking people to remember all their medical care for the past year, people were interviewed several times so that they had a shorter recall period. The second was that instead of expecting people to remember precisely what their medical insurance covered, or what was done at each medical visit, an insurance component and a medical provider component were conducted to obtain that information from the insurance or medical provider. That is, the MEPS is four surveys in one: a household component, a medical-provider component, an insurance component, and a nursing-home component. The nursing-home component adds another unique feature, all of these surveys are of the civilian noninstitutionalized population. Having the nursing-home component at least makes inclusion of the older population, the people who are most likely to use medical services, complete.
The MEPS impact on policy has always been great and has increased as issues such as the cost of medical care and the proportion of the uninsured population have grown as policy issues. One of the early discoveries from the MEPS was that the proportion of the population uninsured at some time during the year was much greater than the proportion uninsured at any one time. That led to a complete reassessment of the uninsured population of the United States. Recent contributions to policy have been estimating the number of children who are eligible for, but not enrolled in, Medicaid; estimating the potential number of children eligible for the State Children's' Health Insurance Program (SCHIP); examining racial and ethnic disparities in medical insurance coverage over the past decade; examining whether medical insurance is an impediment to job mobility; and the potential for participation in medical savings accounts.
There are other population surveys of selected segments of the population. The National Survey of Family Growth, up to now a survey of women of child-bearing age but soon to include men, has informed the government on many aspects of population policy, including the characteristics of people who adopt children. The Health and Retirement Survey, a collaborative project between the National Institute of Aging and the Survey Research Center at the University of Michigan, is a survey of men and women approaching retirement age designed to study the health and economic predictors of their retirement decisions. The Survey of Income and Program Participation, conducted by the U.S. Bureau of the Census, is a longitudinal survey designed to understands people's movement into and out of public programs.
These are all surveys in which the interviewer goes to the individual's home to conduct the interview. Such surveys are expensive. As the cost of conducting household interviews increased, interest in telephone surveys also increased. New techniques for overcoming problems such as multiple telephones in a single household, and techniques for scheduling calls were developed, and telephone surveys are now more widely used than personal interview surveys. They have some disadvantages for health research because the people who are least likely to have telephones are poor people—and they are also most likely to be sick or to have problems accessing medical care. However, used wisely, they can enable data collection that would not be financially possible with household surveys.
BEHAVIORAL RISK FACTOR SURVEILLANCE SYSTEM
One example of a telephone survey is the Behavioral Risk Factor Surveillance System (BRFSS). It is also a repeated cross-sectional survey like the NHIS and the NHSDA, but unlike them it is a system of state surveys that are coordinated by the National Center for Chronic Disease Prevention and Health Promotion at the CDC. The decision as to what questions will be on the next year's questionnaire is made at an annual conference attended by the state coordinators and CDC staff. There is a core of questions asked in all states, optional questions on selected topics that are asked in many states, and space for questions of major interest to that state or, sometimes, a group of neighboring states. The impact on national policy is to provide evidence of the sometimes remarkable differences among the states in important policies, such as smoking. The impact in states that actually use the data is that the states for the first time have data that are relevant to their own state policies. Many states are now using the data for substate areas, such as health planning areas.
These surveys have been in existence for more than a decade because they have proved their worth. Each fills a niche and has a rather fixed formal structure. Yet each has flexibility built into it so that in addition to fulfilling their primary purpose, they can be used to respond to immediate as well as long-term questions.
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