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Study design can dictate
the sampling frame. The sampling frame for telephone surveys such
as the Behavioral Risk Factor
Surveillance Survey (BRFSS) conducted by the Centers of Disease
Control and Prevention consists of persons who have telephones
and who have listings in telephone directories. Individuals without
telephones in their residence are therefore excluded. This survey
is fielded in all 50 states, the District of Columbia, and the
Virgin Islands, and supports state level as well as national analyses.
The documentation for BRFSS includes information on the percentage
of households in each locality who are included in the sampling
frame.
In interpreting data
from this survey it is important to note that while it is a nationally
representative survey, a small subpopulation who may differ is
excluded. This will bias responses to a greater extent for populations
where individuals are less likely to have a telephone. For example,
persons without telephones are known to have lower socioeconomic
status; this is also associated with health status (Groves
et al., 1988). In the future, as more people have cellular
phones and are not listed in phone directories, coverage rates
may decline.
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