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BRFSS Methodology Previous Page

Target Population
Adults 18 years or older who live in a private residence or a college housing unit are asked to take part in the survey. Only one adult per household is randomly selected to be interviewed once the telephone number is verified as a private working phone number. Cell phone numbers are also sampled allowing adults who receive at least 90% of their calls on their cell phone to be included in the sample. Participants are not compensated.


Data Collection
Information is collected through telephone interviews throughout the survey year. A set of randomly generated phone numbers are produced at least four times per year, and the phone numbers are first called to verify if they are residential or a business phone number. If residential, a randomly selected adult in the household is asked to participate. This can result in repeat phone calls to the household in order to get the appropriate (randomly selected) adult to participate. In addition, the 2011 survey and all subsequent years must have at least 20% of the total completed interviews consist of responses from cell phone users. Adults who receive at least 90% of their calls on their cell phone are eligible to be included in the cell phone sample.


Sample Size
Since 2003, the goal of the Virginia BRFSS has been to complete at least 5,000 interviews with Virginia adults annually.



Interview Year

Number of Landline Completions

Number of Cell phone Completions

1997

3,524

1998

3,506

1999

3,502

2000

1,996

2001

2,939

2002

4,392

2003

5,442

2004

5,576

2005

5,232

2006

5, 453

2007

6, 203

2008

5,310

2009

4,807

2010

5,392

2011

5,598

1,007

2012

6,085

1,313



Cell Phone Sampling

Virginia was one of six states that participated in a cell phone sample pilot in 2008. The goal was to complete at least 250 BRFSS interviews with respondents on their cell phones. For participating and completing an interview, respondents were given a ten dollar ($10) Amazon gift card. In 2009 and 2010, Virginia continued to complete at least 250 BRFSS interviews with respondents on their cell phones. The cell phone data from 2008-2010 were not included in the yearly BRFSS datasets. Cell phone data was first included in the BRFSS yearly dataset in 2011.


Stratification
From 1997 to 1999, and again from 2002 through 2010, the Virginia Department of Health (VDH) funded additional data collection to allow stratification of the state by the thirty-five (35) health districts. Approximately 140 interviews were collected annually in each health district.


Links to the thirty-five (35) local health districts websites:


Weighting Methodology
BRFSS data are first weighted for the probability of selection of a telephone number, the number of adults in a household, and the number of telephones in a household. Then post-stratification adjustments are made to account for non-response and non-coverage (households without telephones). For the 2010 dataset and prior surveys post-stratification was based on only age, sex, and region of residence. Beginning with the 2011 dataset, a raking (or iterative proportional fitting) procedure is used for post-stratification adjustment. The use of raking procedures allows post-stratification adjustment to be based on twelve demographic dimensions rather than only three. Including new variables in the weighting process can reduce the potential for selection bias while increasing representation. For a complete explanation of raking procedures see: www.cdc.gov/mmwr/preview/mmwrhtml/mm6122a3.htm

 

Last Updated: 07-23-2013

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