Samples used in the BRFSS must be probability samples in which all households with telephones have a known, nonzero chance of inclusion, as stated in item #1 in Policy Memo 2003.1. All samples come from the Telecordia Technologies database and include all numbers in NXX Types 00, 50, 51, 52, and 54 in the sampling frame.

Disproportionate stratified random sampling (DSS)

With DSS, as implemented in the BRFSS beginning in 2003, telephone numbers are drawn from two strata (lists) that are based on the presumed density of known telephone household numbers. In this design, telephone numbers are classified into strata that are either high density (listed 1+ block telephone numbers) or medium density (not listed 1+ block telephone numbers) to yield residential telephone numbers. Telephone numbers in the high density stratum are sampled at the highest rate. The rate at which each stratum is sampled is called the sampling rate. The ratio of the sampling rate of one stratum to sampling rate of a reference stratum is called the sampling ratio.

DSS Overview

The DSS design attempts to find a way of differentiating, before sampling begins, between a set of telephone numbers that contains a large proportion of target numbers (the high-density block) and a set that contains a smaller proportion of target numbers (the medium-density block). It is possible to create more than two groups, but for BRFSS, only two groups are used. In this way, sampling telephone numbers is more efficient compared to simple random sampling.

See user guide for more information.

BRFSS Weighting Formula FINALWT = STRWT * 1 OVER NPH * NAD * POSTSTRAT

The computational formula above is intended to reflect all the possible factors that could be taken into account in weighting a state's data. Where a factor does not apply its value is set to one. FINALWT is the final weight assigned to each respondent. STRWT accounts for differences in the basic probability of selection among strata (subsets of area code/prefix combinations). It is the inverse of the sampling fraction of each stratum. There is almost never a complete correspondence between strata, which are defined by subsets of area code/prefix combinations, and regions, which are defined by the boundaries of government entities. 1/NPH is the inverse of the number of residential telephone numbers in the respondent's household. NAD is the number of adults in the respondent's household. POSTSTRAT is the number of people in an age-by-gender or age-by-race-by-gender category in the population of a region or a state divided by the sum of the products of the preceding weights for the respondents in that same age-by-gender or age-by-race-by-gender category. It adjusts for non-coverage and non-response and, before 1995, also adjusts for different probabilities of selection by region, where applicable.

Calculation of CHILDWT

CHILDWT = STRWT * 1 OVER NPH * CHILDREN * POSTCH

CHILDWT is the final weight assigned to each child. STRWT accounts for differences in the basic probability of selection among strata (subsets of area code/prefix combinations). It is the inverse of the sampling fraction of each stratum. There is almost never a complete correspondence between strata, which are defined by subsets of area code/prefix combinations, and regions, which are defined by the boundaries of government entities. 1/NPH is the inverse of the number of residential telephone numbers in the respondent's household. CHILDREN is the number of children (less than 18 years of age) in the respondent's household. POSTCH is the number of children in an age-by-gender or age-by-race-by-gender category in the population of a region or a state divided by the sum of the products of the preceding weights for the children in that same age-by-gender or age-by-race-by-gender category. It adjusts for non-coverage and non-response.

Calculation of HOUSEWT

HOUSEWT = STRWT * 1 OVER NPH * POSTHH

HOUSEWT is the weight assigned to each household. STRWT accounts for differences in the basic probability of selection among strata (subsets of area code/prefix combinations). It is the inverse of the sampling fraction of each stratum. There is almost never a complete correspondence between strata, which are defined by subsets of area code/prefix combinations, and regions, which are defined by the boundaries of government entities. 1/NPH is the inverse of the number of residential telephone numbers in the household. POSTHH is the number of households in the population of a region or a state divided by the sum of the products of the preceding weights for the households in that same category. It adjusts for non-coverage and non-response.

ICPSR data undergo a confidentiality review and are altered when necessary to limit the risk of disclosure. ICPSR also routinely creates ready-to-go data files along with setups in the major statistical software formats as well as standard codebooks to accompany the data. In addition to these procedures, ICPSR performed the following processing steps for this data collection:

More information on the BRFSS studies can be found on the

Median overall response rate: 42.4 percent

Please see the Summary Data Quality Report for more information.

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