testing for coverage bias when combining directory-listed and cellphone samples t. m. guterbock, a....
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Testing for Coverage Bias when Combining Directory-Listed And Cellphone Testing for Coverage Bias when Combining Directory-Listed And Cellphone SamplesSamples
T. M. Guterbock, A. Diop, J. M. Ellis, J. L. P. Holmes and K. T. Le, Center for Survey Research, University of T. M. Guterbock, A. Diop, J. M. Ellis, J. L. P. Holmes and K. T. Le, Center for Survey Research, University of VirginiaVirginia
RDD+Cell costs too much!
Cell-only households are increasing.
Researchers are using a dual-frame sample design combining RDD and cell phone frames (“RDD+Cell”).
RDD+Cell costs more than RDD because cell phone interview costs are 2 to 3 times higher than RDD costs.
Random digit dial (RDD) continues to lose efficiency due to lower phone number densities in sampled call groups.
RDD is especially inefficient in local surveys, where households must be screened for location.
Do we really need all that RDD?Cellphone samples today are used to capture underrepresented groups that RDD samples were originally designed to capture.
Modify the RDD+Cell design to use Electonic White Pages sample. The “EWP+Cell” design covers all phone HH except unlisted landline-only.
EWP+CellBenefits DrawbacksLower cost Noncoverage biasGeographic specificityFaster field time
Are noncoverage biases small enough and benefits large enough to support using EWP+Cell?
We showed (AAPOR 2008) that in the 2006 National Health Interview Survey, simulated results from EWP+Cell were very close to RDD+Cell results.
Three “citizen satisfaction” surveys conducted in 2008, in three suburban Virginia counties
Each survey used a triple-frame design: RDD, EWP and cellphone frames
Surveys were similar in content, length and design Percentage of the telephone universe that has cell
phones was estimated separately for each countyFinal data were weighted for estimated cellphone-
only prevalence in each county$10 incentives for cellphones ($5/$10 test in PWC)Triple frame design allows direct test:
RDD+Cell vs. EWP+Cell
www.virginia.edu/surveys
AAPOR Annual Conference
Hollywood, FL, May 2009
But NHIS is a very large , national in-person But NHIS is a very large , national in-person survey. Will these results hold up in smaller survey. Will these results hold up in smaller
local surveys conducted by telephone?local surveys conducted by telephone?
1
3
1
2 2
8
5
7 7
3
1 1
0
1
2
3
4
5
6
7
8
9
-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7
Number
of
Items
Raw Percentage Point Difference: EWP+Cell - RDD+Cell (41 items)
Albemarle County 2008Count of Survey Items by Percentage Point Difference
12
1
8
14
24
13
10
12
1
0
5
10
15
20
25
30
-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7
Number
of
Items
Raw Percentage Point Difference: EWP+Cell - RDD+Cell (77 items)
Chesterfield County 2008Count of Survey Items by Percentage Point Difference
2 2 2
11
17
43
21
0
2
4
6
8
10
12
14
16
18
-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7
Number
of
Items
Raw Percentage Point Difference: EWP+Cell - RDD+Cell (44 items)
Prince William County 2008Count of Survey Items by Percentage Point Difference
RDD+Cell covers all five telephone segments
EWP+Cell covers four of five segments
One example: For this item, the differences in responses were small and within the margins of error for the surveys. Ratings were dichotomized for analysis.
Items with sufficient n sizes were compared across EWP+Cell and RDD+Cell within each survey. Raw percentage differences were rounded and tallied. Most differences are smaller than the survey sampling errors.
Prince William (DC suburbs)
Albemarle (C’ville suburbs)
Chesterfield (Richmond suburbs)
N CPH N CPH N CPH RDD 623 0.82 278 1.12 637 1.16 EWP 693 1.09 334 1.39 980 1.40
CELL 187 0.56 155 0.57 157 0.40 Combined samples 1503 767 1774
Estimated % cell phone only: 19.0% 8.4% 8.0% % of unlisted in RDD: 23.8% 10.1% 17.6%
% unlisted landline only: 2.2% 1.4% 1.3% MOE (weighted triple-frame) ±2.9 ±3.8 ±2.7
County % satisfied with overall county government services
Δ RDD EWP CELL RDD+CELL EWP+CELL
Prince William 89.4 89.3 88.0 89.3 89.4 0.1% Albemarle 90.5 92.6 94.5 92.0 93.5 1.5% Chesterfield 85.5 86.9 85.4 85.5 86.6 1.2%
Assume $33 per interviewing hour CPH Cost Total cost Prince William
EWP+Cell EWP (n=800) 1.09 $24,220 $38,206
save 17% Cell (n=200) 0.56 $13,986 Prince William
RDD+Cell RDD (n=800) 0.82 $32,195
$46,091 Cell (n=200) 0.56 $13,986
Albemarle EWP+Cell
EWP (n=800) 1.39 $18,993 $32,772 save 12% Cell (n=200) 0.57 $13,779
Albemarle RDD+Cell
RDD (n=800) 1.12 $23,571 $37,350
Cell (n=200) 0.57 $13,779 Chesterfield
EWP+Cell EWP (n=800) 1.40 $18,857 $37,557
save 9% Cell (n=200) 0.40 $18,700 Chesterfield
RDD+Cell RDD (n=800) 1.16 $22,759
$41,459 Cell (n=200) 0.40 $18,700
Note: Cellphone costs include $10 incentive and $1 processing
2CELL + ULL
17.7%
4CELL + LLL
34.3%5
LLL ONLY17.2%
3ULL ONLY
14.2%1CELL ONLY
16.6%
Cell
Overlap
EWP
1CELL ONLY
16.6%
2CELL + ULL
17.7%
4CELL + LLL
34.3%
3ULL ONLY
14.2%
5LLL ONLY
17.2%“ULL”=Unlisted
Landline
“LLL”=Listed Landline
““CPH” = Completions per hourCPH” = Completions per hour
Prince William County 2008
1CELL ONLY
16.0%
2CELL + ULL
24.2%
3ULL ONLY
2.2%
4CELL + LLL
54.6%
5LLL ONLY
3.0%
Cell
Overlap
EWP
Albemarle County 2008
1CELL ONLY
8.9%
2CELL + ULL
11.3%3
ULL ONLY1.4%
4CELL + LLL
71.2%
5LLL ONLY
7.2%
Cell
Overlap
EWP
Chesterfield County 2008
1CELL ONLY
8.6%
2CELL + ULL
16.0%
3ULL ONLY
1.3%
4CELL + LLL
68.8%
5LLL ONLY
5.3%
Cell
Overlap
EWP
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