an overview of the north carolina behavioral risk factor surveillance system (brfss) presentation to...
TRANSCRIPT
An Overview of the North Carolina Behavioral Risk Factor Surveillance System (BRFSS)
Presentation to the
State Health Director's Conference
January 23, 2014
State Center for Health StatisticsDivision of Pubic HealthNC Dept. of Health & Human Services
Presentation Outline
How the survey is done Questionnaire development Sampling Data Collection Weighting
Future developments Demonstrate how to access results Q&A
State Center for Health StatisticsDivision of Pubic HealthNC Dept. of Health & Human Services
Timeline for 2014 BRFSSExternal review of proposed new/revised questions2012
2013 State Coordinators vote on proposed questions
CDC field tests questionnaire
CDC Core & Optional Modules checked and finalized
State-added questions reviewed and finalized
CATI coding developed and checked
Interviewers trained
2014 Conduct interviews January through December
CDC sends final weighted data to NC
SCHS reviews data and produce web tables
2015
BRFSS QUESTIONNAIRE
Questionnaire Organization
Each years survey is divided into three main parts
CDCCore
Questions
CDCOptionalModules
State-Added
Questions
Mandated by CDC;must ask all questions exactly as written
States choose whichmodules they willadminister; must askall questions exactlyas written
Developed by eachstate’s coordinator
The Core The CDC Division of Behavioral Surveillance (DBS) works with
other CDC programs to develop questions for the core & optional modules
Proposed questions undergo two rounds of cognitive testing State Coordinators have input via
Participation in State Working Group Participation as external reviewer for proposed questions Vote on proposed questions taken at Annual Conference
Questions rotate in & out of core on a fixed schedule Just adopted a new 5-year plan for the core
CDC Optional Modules
Process for developing optional modules is similar to the core
CDC programs pay DSB for space on the BRFSS
So the selection of optional modules available varies each year
State-Added Questions
May include Questions from other surveys, including questions
on CDC Optional Modules Questions written by state staff
Each state has a process for soliciting proposed questions
Survey time is a very scarce resource When telephone interviews run past 15 to
20 minutes, Break-offs increase Data quality suffers as people say whatever
comes to mind so you’ll leave them alone! Some cell phone respondents are more
sensitive to length because they pay by the minute
Pew Research Center successfully does 20 minute cell phone interviews
The 2013 NC BRFSS interview averaged 29 minutes 17 minutes of that is take up by Core questions and an
expanded Optional Module on Health Care Access “Core creep” – expansion of the length of the core – is a
major issue with state coordinators We have been trying to cut down on state-added
and CDC Optional Modules to shorten the interview
SAMPLING
Random Digit Dialing (RDD) Surveys 4 digit numbers are generated at random
within each combination of area code and phone exchange within a geographic area
Resulting numbers are screened to identify non-working numbers
Results in a random sample of telephone numbers for a given geographic region
BRFSS uses a Dual-Frame RDD Sample Landline Frame
Numbers generated within area code/exchange combinations for landline telephones
Telco companies share more information regarding these numbers Most importantly where the phone is located
Cell Phone Frame Numbers generated within area code/phone
exchange combinations for cell phones Cell phone companies share little information
about these numbers Little information on where owner of phone lives until
they are interviewed
Increase in “Cell Phone Only” (Wireless) Households Roughly 38% of adults as of
the end of 2013. These folks are:
Younger More are minorities Less affluent Have some significantly
different health conditions & behaviors
Must sample this population to avoid biased estimates
DATA COLLECTION
“BRFSS is a process, not a project” Survey runs throughout calendar year
Each month we receive separate landline and cell phone samples (~8,000 phone numbers total)
To complete each month’s “study” Each landline number is called up to 15 times Each cell phone number is called up to 8 times
We call seven days a week around 330 days every year
More difficult to reach cell phone respondents In the landline sample
Get one completed interview every 1.4 hours of interview time
Perform 38 dialings per completed interview 4,600 sample records yield ~900 completed interviews
Cell Get one completed interview for every 1.7 hours Perform 97 dialings per completed interview 3,200 sample records yield ~100 completed interviews
Bottom Line: We have to call many, many more cell phone numbers before finding someone who will complete the interview
WEIGHTING
Why Weight?
We weight survey data to make our sample better match the population
Some observations “get counted” more than others
BRFSS Weighting Systems
The old BRFSS system used gender, age, race/ethnicity, & region within state to adjust the final results.
The new rake weights adds adjustment by education level, marital status, renter/owner status & phone source (landline vs. cell phone)
The new “raked” weights should improve the representativeness of the sample, particularly regarding socioeconomic status
The new weights, together with adding cell-phone interviews, produces different estimates for some health indicators
Percent of Adults Who Are Current Smokers, 2010
19.78
24.12 25.26
0
5
10
15
20
25
30
Landline only, old weight Landline only, raked weight Landline & cell, raked weight
Sample & Weight Used
Percentage
Some estimates change a lot:
Estimate increases by ~ 5.5 percent
Binge Drinking
11 11.16
14.28
0
2
4
6
8
10
12
14
16
Landline only, old weight Landline only, raked weight Landline & cell, raked weight
Sample & Weigh Used
Per
cen
tag
e
Estimate increases by ~ 3.3 percent
Some estimates change very little:
Estimate increases by ~ 1.0 percent
Percentage of Adults Diagnosed with Diabetes, 2010
9.77
11.6210.74
0
2
4
6
8
10
12
14
Landline only, old weight Landline only, raked weight Landline & cell, raked weight
Sample & Weight Used
Per
cen
tag
e
Percentage of Adults Getting Recommended Amout of Physical Activity, 2009
46.4143.98 45.46
0
510
15
2025
30
35
4045
50
Landline only, old weight Landline only, raked weight Landline & cell, raked weight
Sample & Weight Used
Percentage
Estimate increases by ~ 0.9 percent
FUTURE DEVELOPMENTS
Change to Geographic Strata
Beginning in 2014, geographic strata will be based on Area Health Education Center regions Able to stratify both landline and cell phone
samples for these area
We will produce estimates for State as a whole Eastern, Piedmont & Western Carolina AHECS Counties when possible
At least 500 completed interviews in the sample
HOW TO ACCESS RESULTS
Data for a calendar year are combined and analyzed
Results for state and sub-regions are posted to SCHS Web page Main SCHS Web Page
http://www.schs.state.nc.us/ NC BRFSS Web Page
http://www.schs.state.nc.us/units/stat/brfss/
Contact Information: James Cassell
Head of Survey Operations & BRFSS CoordinatorState Center for Health StatisticsNorth Carolina Division of Public Health2422 Mail Service CenterRaleigh, NC 27699-2422
Voice: 919-855-4485Fax: 919-715-7899Email: [email protected]
NC BRFSS Web Page http://www.schs.state.nc.us/units/stat/brfss/
State Center for Health StatisticsDivision of Pubic HealthNC Dept. of Health & Human Services