Adaptive survey designs to minimize survey mode effects – a case study on the Dutch Labor Force Survey
5. DiscussionAdaptive survey designs to minimize survey mode effects – a case study on the Dutch Labor Force Survey
5. Discussion
We constructed a multi-mode optimization problem that
extends the framework of adaptive survey designs to mixed-mode survey
(re)designs. This framework is especially useful when it is anticipated that
method effects due to a change of mode design may impact the comparability and
accuracy of statistics. To our best knowledge, this is the first research
attempt of its kind and can be used as a basis for minimizing method effects
subject to costs and other constraints.
In the optimization model, we included three quality
criteria, one cost criterion and one logistical criterion. The quality criteria
were the numbers of respondents in sampling strata, which acts as a surrogate
for precision, the absolute adjusted overall method effect, which is the level
shift caused by the design relative to the benchmark design and may be viewed
as comparability in time, and the maximal absolute difference in method effects
over important subpopulations, which may be viewed as comparability over
population domains. The cost criterion is the total budget of the survey. The
logistic criterion is the sample size, which needs to be limited in order to
avoid a quick depletion of the sampling frame. The third quality criterion, the
maximal absolute difference in subpopulation method effects, is nonlinear in
the decision variables (the strategy allocation probabilities) and makes the
optimization problem computationally complex. Although this criterion
complicates the problem, it is a useful constraint that is often put forward by
survey analysts and users. In regular redesigns, this criterion is often not
considered and the Dutch LFS mixed-mode design leads to relatively large
differences in method effects between subpopulations. Clearly, some of the
criteria may be omitted and other quality, cost or logistical criteria may be
added. In a follow-up on this research at Statistics Netherlands, various other
criteria, mostly logistical, are considered.
In the optimization model, the focus was on maximizing
quality, reflected by comparability in time, subject to cost constraints and
other constraints on quality and logistics. The objective of the optimization
may, however, be changed and each of the constraints could function as the
objective. For instance, one may minimize cost subject to quality and
logistical constraints. One may also take a wider approach and perform several
optimizations for different budget and quality levels in order to derive an informative
multidimensional view on which a decision can be based.
Our attempt must be seen as merely a first step towards
adaptive mixed-mode survey designs. There are various methodological and
practical issues that need to be resolved. First, our approach is suited for
surveys with only a few key statistics. For each of these statistics, an
optimization can be performed and a weighted decision can be made. When a
survey has a wide range of statistics, such an approach is not feasible.
Second, the optimization leans heavily on the accuracy of its input parameters,
i.e., estimated response probabilities, registered-telephone probabilities,
cost parameters and mode effects in this case. It is important to assess the
sensitivity of the optimization results to the accuracy of these parameters. It
may be hypothesized that the objective function is relatively smooth with
respect to these parameters, however, it is still important to perform
sensitivity analyses. Third, it is essential to consider the sampling variation
of the realized quality and costs of the optimized design when multiple waves
of a survey are conducted. Such variation may be large and downsize the value
of a precise optimization. Fourth, once nonlinear criteria are added to the
problem, one has to rely on advanced solvers in statistical software. Even when
using such solvers, convergence to global optimum is usually not assured and
one has to be satisfied with local optima. For this reason, it is important to
choose a useful set of starting points, including starting points that
correspond to current designs. The practical issues concern the number of
population strata, the number of strategies and the coordination to other
surveys. Although survey administration systems and tools may support adaptive
survey designs, such designs are harder to monitor and analyze. Furthermore,
the tailoring of survey modes affects the size and form of interviewer
workloads; interviewers may get only a specific range of subpopulations.
An important aspect of adaptive survey designs is the
use of estimates for all kinds of input parameters such as response
propensities, variable costs per sample unit and method effects between
designs. Such estimates may not be readily available and there may only be weak
historic survey data to support estimation. There are then four options: search
for similar surveys that have historic support, be modest and restrictive in
the choice of design features, perform a transitional period in which pilot
studies and parallel runs are conducted, and develop a framework for learning
and updating of parameters. In particular, designs with
as one of the modes may still lack historic
support for estimation in many countries, see, e.g., Mohorko, de Leeuw and Hox (2013). We also note that input
parameters may gradually change in time, so that continuous updating will be
needed. However, all of this is no different from a non-adaptive survey, except
that now estimates are needed for relevant subpopulations instead of the overall
population alone. Finally, we note that optimized adaptive designs, like
optimized non-adaptive designs, provide an average, expected quality and costs.
Due to sampling variation, the realized quality and costs will vary and
unforeseen events may lead to deviations. Hence, monitoring and reacting to
unforeseen events remain necessary.
Future research needs to address robustness of adaptive
survey designs and should investigate other quality, cost and logistical
criteria. It is also important that this study is replicated in order to
evaluate whether the investment in terms of additional data collection and in
terms of explicit optimization is worth the effort. The ultimate goal of this
research is a data collection design strategy that allows for learning and
updating optimization input parameters and that supports effective and
efficient cost-benefit analyses in mixed-mode (re)designs. A Bayesian approach
seems most promising for this purpose.
Acknowledgements
The authors would like to thank dr. Sandjai Bhulai (VU
University Amsterdam) for his constructive comments on the mathematical
framework presented in the current paper. The authors also thank Boukje Janssen
(CBS) and Martijn Souren (CBS) for processing the raw field data for analysis
and Joep Burger (CBS) for his comments that helped improve this paper.
Appendix A
Estimates of input parameters
In Section 4.4, we explain the estimation of input
parameters for strategies that are observed only partially in the parallel
runs. Here, we give the estimates for the response propensities, telephone
registration propensities, variable costs per sample unit and adjusted method
effects. Standard errors for all parameters were estimated using bootstrap
resampling.
Table A2 presents the estimated response propensities
from available data and their corresponding
standard errors. Table A1 shows the estimated propensity for a registered phone
Table A1
Estimated propensities for registered phone for group
with the corresponding standard errors given in brackets Table summary
This table displays the results of Estimated propensities for registered phone for group XXXX with the corresponding standard errors given in brackets. The information is grouped by XXXX (appearing as row headers), XXXX (appearing as column headers).
38.1%
76.4%
30.2%
22.4%
60.0%
38.9%
32.0%
53.4%
62.4%
(0.9)
(1.6)
(2.0)
(2.2)
(1.1)
(0.7)
(1.3)
(0.6)
(1.2)
Table A2
Estimated response propensities per strategy
and group
with the corresponding standard errors given in brackets Table summary
This table displays the results of Estimated response propensities per strategy XXXX and group XXXX with the corresponding standard errors given in brackets . The information is grouped by XXXX (appearing as row headers), XXXX (appearing as column headers).
23.2%
23.6%
15.5%
10.8%
27.9%
27.7%
17.5%
36.7%
22.4%
(0.3)
(0.6)
(0.6)
(0.6)
(0.4)
(0.2)
(0.5)
(0.2)
(0.5)
12.2%
31.4%
8.5%
4.7%
19.7%
13.3%
7.2%
18.1%
21.2%
(0.5)
(1.1)
(0.8)
(0.8)
(0.6)
(0.4)
(0.5)
(0.4)
(0.8)
20.8%
41.3%
15.2%
8.6%
31.1%
23.8%
14.3%
33.3%
37.5%
(0.6)
(1.1)
(1.0)
(1.0)
(0.7)
(0.5)
(0.7)
(0.5)
(0.9)
43.5%
53.5%
42.2%
34.1%
45.1%
45.3%
35.9%
46.7%
54.6%
(1.5)
(1.7)
(2.4)
(2.4)
(1.1)
(0.9)
(1.5)
(0.7)
(1.4)
52.4%
58.3%
51.0%
41.2%
51.2%
54.9%
46.0%
56.8%
61.4%
(1.3)
(1.6)
(2.5)
(2.2)
(1.1)
(0.8)
(1.4)
(0.7)
(1.3)
28.3%
41.0%
20.2%
13.9%
36.3%
34.0%
20.8%
44.5%
23.1%
(0.4)
(0.8)
(0.7)
(0.8)
(0.4)
(0.3)
(0.5)
(0.3)
(0.5)
32.8%
48.4%
23.8%
17.5%
42.1%
41.1%
25.8%
52.1%
24.4%
(0.4)
(0.7)
(0.8)
(0.9)
(0.5)
(0.3)
(0.6)
(0.3)
(0.5)
46.3%
57.7%
38.6%
32.7%
50.0%
51.0%
39.3%
58.9%
50.0%
(0.5)
(1.0)
(1.0)
(1.0)
(0.6)
(0.4)
(0.7)
(0.4)
(0.5)
49.8%
58.3%
43.4%
36.6%
52.6%
54.7%
44.3%
62.0%
54.2%
(0.5)
(0.9)
(0.9)
(0.9)
(0.5)
(0.4)
(0.6)
(0.4)
(0.5)
For the method effect
two benchmarks were selected after
consultation with practitioners, i.e.,
and
where
represents the average unemployment rate
estimated via the indicated survey mode. Tables A3 and A4 present the estimated
method effects against the two benchmarks including their standard errors.
The estimates for the variable costs per sample unit
plus estimated standard errors are given in Table A5. The costs are
expressed relative to the
strategy, which is set at one.
Table A3
Estimated method effects against benchmark
with the corresponding standard errors given in brackets Table summary
This table displays the results of Estimated method effects against benchmark XXXX with the corresponding standard errors given in brackets. The information is grouped by XXXX (appearing as row headers), XXXX (appearing as column headers).
1.5%
0.0%
-2.3%
-4.5%
0.9%
-0.4%
-2.2%
0.6%
-0.4%
(1.0)
(0.5)
(1.5)
(3.1)
(0.7)
(0.4)
(1.5)
(0.5)
(0.6)
-0.2%
-0.1%
-2.6%
-6.8%
-1.0%
-0.9%
-1.1%
0.2%
-1.3%
(0.7)
(0.1)
(0.9)
(1.8)
(0.4)
(0.3)
(1.1)
(0.4)
(0.4)
-0.1%
-0.1%
-2.3%
-4.9%
-0.6%
-1.0%
-0.8%
-0.2%
-1.2%
(0.7)
(0.1)
(0.8)
(1.7)
(0.4)
(0.3)
(1.0)
(0.3)
(0.4)
-0.5%
-0.1%
0.0%
0.7%
-0.1%
0.0%
0.5%
0.3%
0.1%
(0.3)
(0.1)
(0.4)
(0.6)
(0.1)
(0.1)
(0.3)
(0.1)
(0.1)
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
(0.0)
(0.0)
(0.0)
(0.0)
(0.0)
(0.0)
(0.0)
(0.0)
(0.0)
0.9%
0.0%
-2.4%
-3.4%
-0.1%
-0.7%
-4.4%
0.9%
-0.7%
(1.0)
(0.4)
(1.5)
(3.7)
(0.6)
(0.5)
(1.9)
(0.5)
(0.6)
0.9%
-0.1%
-3.7%
-1.7%
0.5%
-0.7%
-3.0%
0.6%
-0.4%
(0.9)
(0.3)
(1.4)
(3.2)
(0.7)
(0.4)
(1.4)
(0.5)
(0.6)
0.7%
0.0%
-1.2%
-1.6%
0.6%
-0.3%
-1.0%
0.5%
-0.2%
(0.6)
(0.3)
(0.8)
(1.4)
(0.5)
(0.3)
(0.8)
(0.3)
(0.3)
0.9%
0.0%
-1.2%
-2.0%
0.6%
-0.3%
-1.2%
0.4%
-0.2%
(0.6)
(0.3)
(0.8)
(1.4)
(0.5)
(0.3)
(0.8)
(0.3)
(0.3)
Table A4
Estimated method effects against benchmark
with the corresponding standard errors given in brackets Table summary
This table displays the results of Estimated method effects against benchmark XXXX with the corresponding standard errors given in brackets. The information is grouped by XXXX (appearing as row headers), XXXX (appearing as column headers).
1.0%
0.1%
-0.8%
-1.4%
0.8%
0.1%
-1.2%
0.5%
0.1%
(0.5)
(0.3)
(0.9)
(1.8)
(0.4)
(0.2)
(0.8)
(0.2)
(0.3)
-0.6%
-0.1%
-1.0%
-3.7%
-1.2%
-0.5%
-0.1%
0.1%
-0.8%
(0.3)
(0.2)
(0.6)
(1.4)
(0.2)
(0.2)
(0.8)
(0.2)
(0.2)
-0.6%
-0.1%
-0.8%
-1.7%
-0.7%
-0.5%
0.2%
-0.3%
-0.6%
(0.2)
(0.2)
(0.5)
(1.0)
(0.2)
(0.1)
(0.5)
(0.1)
(0.2)
-1.0%
-0.1%
1.6%
3.8%
-0.2%
0.5%
1.5%
0.2%
0.6%
(0.7)
(0.2)
(0.8)
(1.6)
(0.4)
(0.2)
(0.8)
(0.3)
(0.3)
-0.5%
0.0%
1.6%
3.1%
-0.1%
0.5%
1.0%
-0.1%
0.5%
(0.5)
(0.2)
(0.7)
(1.4)
(0.4)
(0.2)
(0.7)
(0.3)
(0.3)
0.4%
0.0%
-0.9%
-0.3%
-0.2%
-0.2%
-3.4%
0.7%
-0.1%
(0.5)
(0.3)
(1.0)
(2.9)
(0.4)
(0.3)
(1.5)
(0.3)
(0.4)
0.5%
0.0%
-2.1%
1.5%
0.4%
-0.2%
-2.0%
0.5%
0.1%
(0.4)
(0.2)
(0.8)
(2.0)
(0.4)
(0.2)
(0.8)
(0.2)
(0.3)
0.3%
0.0%
0.4%
1.5%
0.5%
0.2%
0.0%
0.4%
0.3%
(0.2)
(0.1)
(0.3)
(0.6)
(0.2)
(0.1)
(0.3)
(0.1)
(0.1)
0.4%
0.0%
0.4%
1.1%
0.5%
0.2%
-0.2%
0.3%
0.3%
(0.1)
(0.1)
(0.3)
(0.5)
(0.2)
(0.1)
(0.3)
(0.1)
(0.1)
Table A5
Estimated relative unit costs (in euros) per strategy
and group
with the corresponding standard errors given in brackets Table summary
This table displays the results of Estimated relative unit costs (in euros) per strategy XXXX and group XXXX with the corresponding standard errors given in brackets . The information is grouped by XXXX (appearing as row headers), XXXX (appearing as column headers).
0.03
0.04
0.04
0.03
0.04
0.03
0.03
0.03
0.03
(0.0)
(0.0)
(0.0)
(0.0)
(0.0)
(0.0)
(0.0)
(0.0)
(0.0)
0.11
0.15
0.10
0.09
0.13
0.11
0.09
0.12
0.14
(0.1)
(0.1)
(0.1)
(0.1)
(0.1)
(0.1)
(0.1)
(0.0)
(0.1)
0.13
0.17
0.11
0.10
0.15
0.14
0.11
0.16
0.20
(0.1)
(0.1)
(0.1)
(0.1)
(0.1)
(0.1)
(0.1)
(0.1)
(0.2)
0.84
0.89
0.83
0.82
0.86
0.84
0.81
0.84
0.89
(0.4)
(0.5)
(0.5)
(0.8)
(0.3)
(0.2)
(0.5)
(0.2)
(0.5)
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
(0.6)
(0.6)
(0.7)
(1.1)
(0.4)
(0.3)
(0.6)
(0.2)
(0.5)
0.08
0.11
0.09
0.09
0.09
0.08
0.08
0.07
0.07
(0.0)
(0.1)
(0.1)
(0.1)
(0.0)
(0.0)
(0.0)
(0.0)
(0.0)
0.09
0.12
0.10
0.10
0.10
0.09
0.09
0.08
0.07
(0.1)
(0.1)
(0.1)
(0.1)
(0.1)
(0.0)
(0.1)
(0.0)
(0.0)
0.60
0.66
0.64
0.70
0.59
0.56
0.65
0.51
0.61
(0.3)
(0.7)
(0.6)
(0.8)
(0.4)
(0.3)
(0.5)
(0.2)
(0.4)
0.71
0.71
0.80
0.84
0.73
0.68
0.81
0.62
0.71
(0.4)
(0.7)
(0.9)
(1.2)
(0.6)
(0.4)
(0.8)
(0.3)
(0.6)
Appendix B
Overview optimization results
In Section 4.5 we illustrate our approach to solve the
multi-mode optimization problem for a range of input parameters. Tables B1 and B2
give a brief overview of the optimization results.
Table B1
Overview optimization results linear programming formulation - minimize costs Table summary
This table displays the results of Overview optimization results linear programming formulation - minimize costs. The information is grouped by Sample
size (appearing as row headers), Objective
value, Benchmark, Method
effect, Max
difference
in mode
effects and Response
rate (appearing as column headers).
Sample size
Objective value
Benchmark
Method effect
Max difference in mode effects
Response rate
9,500
123,748.50
0.16%
2.06%
48.0%
0.29%
3.31%
11,000
88,408.95
0.05%
5.97%
39.9%
0.19%
2.98%
12,500
82,270.72
0.08%
5.97%
36.9%
0.21%
2.98%
15,000
74,350.44
0.12%
5.97%
29.4%
0.25%
2.39%
Table B2
Overview optimization results nonlinear problem - minimize average method effect in LFS Table summary
This table displays the results of Overview optimization results nonlinear problem - minimize average method effect in LFS. The information is grouped by XXXX (appearing as row headers), XXXX (appearing as column headers).
9,500
160,000
1%
0.155%
0.5%
Infeasible
0.25%
Infeasible
0.170%
170,000
1%
0.131%
0.5%
Infeasible
0.25%
Infeasible
0.170%
180,000
1%
0.100%
0.5%
Infeasible
0.25%
Infeasible
0.170%
12,000
160,000
1%
0.097%
0.5%
0.119%
0.25%
0.123%
0.046%
0.046%
0.046%
170,000
1%
0.076%
0.5%
0.093%
0.25%
0.101%
0.036%
0.036%
0.036%
180,000
1%
0.009%
0.5%
0.058%
0.25%
0.095%
0.014%
0.014%
0.014%
15,000
160,000
1%
0.051%
0.5%
0.094%
0.25%
0.112%
0.006%
0.006%
0.006%
170,000
1%
0.020%
0.5%
0.080%
0.25%
0.097%
0.004%
0.004%
0.004%
180,000
1%
0.005%
0.5%
0.058%
0.25%
0.095%
0.000%
0.000%
0.000%
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