Notes for Data Users

1998 Data Limitations

This report consolidates the most current data on selected risk factors and preventive health measures for states, the District of Columbia and Puerto Rico. The information was obtained from the data files of individual states.

All states use probability-based methods to select their sample. The BRFSS standard for sample designs is that the sample must be justifiable as a probability sample of all households with telephones in the state. All participating areas except Alaska, California, and Hawaii met this criterion in 1998. For data year 1998, eleven states used the Mitofsky-Waksberg method of sampling. Thirty-seven states used a disproportionate stratified sample (DSS) design. Puerto Rico used a simple random sample design. The three remaining states–Alaska, California, and Hawaii–used other designs.

Alaska
Alaska's sample design is made up of three random digit-dialed strata and four listed strata, where telephone numbers are selected from a list of putative household telephone numbers. The sampling frame contains all of the household numbers in the random digit-dialed strata and an estimated 45% of all household numbers in the listed strata. This represents an exclusion of approximately 9% of all residential telephone numbers in Alaska.

California
California, in July through December 1998, used a sample design in which only telephone numbers from hundred blocks with one or more listed household numbers were included in the sampling frame. Such hundred blocks are estimated to contain 97.8% of all household numbers in California. Telephone numbers from this frame were selected with an equal probability.

Other areas
In a few states, a portion of sample records intended for use during one month may have been completed in another month. This deviation should only affect analyses based on monthly, rather than annual, data.

Other 1998 limitations of the data
In addition to departing from the standard for sample designs, California modified the wording of mammography and Papanicolaou (PAP) test questions, and is therefore excluded from those tables in the report. California also asked the HIV/AIDS section questions to persons 18-44 years of age rather than to those 18-64 years of age as specified, and is therefore not included in the tables for this topic.

Although almost all states collect data monthly, the annual number of interviews ranged from 1616 in Maine to 6005 in Texas in 1998. Estimates for some states are therefore based upon smaller sample sizes, and for rare events (e.g. diabetes), may yield unstable estimates. Maryland did not collect data in January, October, November and December. Some items, including drinking and driving, and obesity, are seasonally affected, and estimates for these items may be biased, especially for Maryland's subpopulations.

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This page last reviewed December 11, 2008

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