BRFSS Annual Survey Data
Survey Data and Documentation
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. |