The model-based estimates of important cancer risk factors and screening behaviors are obtained by combining the responses to the following two surveys.
Both data sources have advantages and disadvantages. The BRFSS is a larger survey (during 1997-2003, approximately 2000-4000 sample adult respondents per state per year and approximately 150,000-200,000 sample adult respondents nationally per year. Currently it interviews more than 400,000 sampled adults per year), and almost every county has some respondents in the survey; but it has lower response rates than the NHIS, and it does not include subjects who live in households with no telephones.
The NHIS is a smaller survey (approximately 30,000-40,000 sample adult respondents nationally per year), but it includes both telephone and non-telephone households and has higher response rates than the BRFSS. The NHIS is an area survey that uses face-to-face interviewing for data collection. Counties (or groups of counties) are the areas sampled at the first stage. This sampling step helps to keep the interviewer travel cost from being excessive. The most populous counties are all included in the NHIS sample, and all other counties have a chance to be selected into the sample at the beginning of a sample design period. The NHIS sample for a sample design period is concentrated in approximately 800 counties, so approximately three quarters of the counties have no sample. At the second stage, respondents are sampled within the selected counties. In most counties, BRFSS has larger sample sizes than NHIS; however, for large population counties in heavily populated states, NHIS may actually have larger sample sizes than BRFSS.
The BRFSS is a state-based system of telephone health surveys, established in 1984 by the Centers for Disease Control and Prevention (CDC). Every month, data are collected from a random representative sample of adults aged 18 years and older in each state on behaviors that place health at risk, on clinical preventive health practices, and on access to health care and use of health care services. BRFSS is conducted by all 50 states, the District of Columbia, Puerto Rico, the Virgin Islands, and Guam, with technical assistance from CDC. Since 2005, more than 350,000 adult interviews are completed each year, making the BRFSS the largest telephone health survey in the world. For most states, it is the only source of recent and accurate health-related data for their state. States use BRFSS data to identify emerging health problems, to establish health objectives and track their progress toward meeting them, and to develop and evaluate public health policies and programs to address identified problems.
Downloadable survey data files and a collection of documents providing technical and statistical information regarding the BRFSS, such as codebooks, calculated variables, comparability, and sample information, are available on the BRFSS Web site. This project used internal (and confidential) datasets that identify all counties, while the downloadable survey data only identifies counties with 50+ respondents for the years prior to 2006. For 2006 and forward, the downloadable survey data only identifies counties with 50+ respondents and with adult population over 10,000.
The BRFSS questionnaire is comprised of core questions and optional modules. There are three types of core questions. Fixed core questions are asked every year. Rotating core questions are asked every other year. Emerging core questions typically focus on "late-breaking" health issues. All states must ask all core questions. The optional modules are either standardized questions developed by the CDC that cover additional health topics, or more detailed questions on a health topic from the core. Each year, states must choose which optional modules they will use based on the data needs of their state.
The NHIS is the principal source of information on the health of the population of the United States and is one of the major data collection programs of the National Center for Health Statistics (NCHS), which is part of the Centers for Disease Control and Prevention (CDC). The NHIS was initiated in July 1957. In 1996, a substantially revised NHIS questionnaire began field testing. This revised questionnaire was implemented in 1997 and has improved the ability of the NHIS to provide important health information.
The main objective of the NHIS is to monitor the health of the United States population through collecting and analyzing data on a broad range of health topics. A major strength of this survey is its ability to provide health information by many demographic and socioeconomic characteristics. The NHIS covers the civilian noninstitutionalized population of the United States. Sample addresses include households and noninstitutional group housing such as college dormitories.
The NHIS, implemented since 1997, has Core questions and Supplements. The Core questions remain largely unchanged from year to year and allow for trends analysis and for pooling of data from multiple years to increase sample size for analytic purposes. The Core contains four major components: Household, Family, Sample Adult, and Sample Child. Topics covered in Supplements are Cancer Screening, Complementary and Alternative Medicine, Children's Mental Health, and Healthcare Utilization, and data needed to track Healthy People 2000 and 2010 objectives. Inclusion of Supplements is dependent on Departmental data needs, priorities, and funding.
Questionnaires, datasets, and related documentation from the NHIS are available for viewing and/or downloading via the Internet. We used internal (and confidential) datasets which identify all counties and are located at NCHS.