Dual Frame Approach refers to the methodology of combining landline and cell phone numbers in order to account for the different mobile/landline penetration within a certain sampling frame. Several methods do exist on how to actually use the framework, e.g. How to handle households that own both landline and mobile telephones. Nevertheless, there are enough reasons to actually avoid landline numbers and use mobile only, or a dual-frame approach

1. SAMPLE SOLUTIONS
CHOICE OF SAMPLING LANDLINE VS MOBILE

3. Introduction
Dual Frame Approach
Dual Frame Approach refers to the methodology of combining landline and cell phone numbers
in order to account for the different mobile/landline penetration within a certain sampling frame.
Several methods do exist on how to actually use the framework, e.g. How to handle households
that own both landline and mobile telephones. Nevertheless, there are enough reasons to actually
avoid landline numbers and use mobile only, or a dual-frame approach
When what to use ?
When clients think of targeting a population within an emerging market, we often receive RFQ´s for
landline numbers since the main advantage seems to be the possibility of geographic tracking, thus
where a person is located. However in some market, the advantages for mobile sample outweigh
its disadvantage. This paper will analyze when what to use.
About Sample Solutions
Sample Solutions Europe is the premier global provider of sampling solutions for survey research.
SAMPLE SOLUTIONS EUROPE offers access to more than 50 million business-to-business records
for market research and can deliver RDD sample for over 25 markets. Sample Solutions Europe was
established by a group of people with decades of experience in the (telephonic) research indus-
try. The lack of local sampling knowledge from the main players in the sample industry (for RDD
sampling), and the lack of details when providing B2B sample, led to the establishment of Sample
Solutions Europe. We aim to provide better, and more detailed, sample, being it RDD or B2B, than
any other multi-market sample provider out there, at the best price-quality ratio possible. This
philosophy has lead to more and more clients from the international research industry finding their
way to Sample Solution Europe for their phone samples.
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4. Some Mobile Myths
On first glance, it seems to be more expensive to use mobile sample for calling
rather than landline sample. Calling mobile phones is often more expensive than
calling landlines. Also, it takes roughly 6 times more (working) mobile numbers
to reach the same target interviews, compared to mobile numbers. Lastly, the
targeting by region is not always possible, making it difficult to fill regional quo-
tas, especially towards the end of a study.
“Mobile phone numbers are more
costly and harder to reach, so why
use mobile?”
Before deciding on the sample it is essential to first conduct a small research on
attributes of the target population. These factors are the local population data,
mobile penetration, landline penetration and geographic circumstances. A good
start is the CIA Worldfactbook which provides most of this data, an overview of
landline and mobile penetration is provided in Appendix A. Based upon the pen-
etration data for landline and mobile, an informed decision can be made what
source to use. Also a small excursion to numbering frames is needed.
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5. Get the whole picture!
When looking at Ireland, initially one would estimate that in terms of landline
penetration (43%), it seems reasonable to conduct a study with landline numbers
only from a practical point of view (methodological is a whole other story, which
we won’t go into within this paper). However as a result of the deregulation of
the telecommunication sector in Ireland, the main provider Eircom has first of
all seen a decrease of landline penetration from 82% to 69% and the trend will
continue. Furthermore many landline users changed to different providers which
have different numbering blocks allocated.
Figure 1: Mobile and Landline Penetration for several sample countries
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6. What to choose ?
As a result the landline penetration per numbering block (eg. 1000) has been
fallen drastically and thus leads to a high percentage of dead (abandoned) num-
bers. Thus for call-centers not making use of predictive dialers it would be rec-
ommended to use mobile sample instead of landline numbers.
_______________________________________________________________
“There is no exact mathematical equation which indicates
preference for landline or mobile sample.”
_______________________________________________________________
This is due to the fact that when using auto-dialer or power dialer, a lot of calling
time is used for dialing numbers in a row, thus waiting for working numbers to
appear. With a predictive dialer several numbers are dialed in parallel thus sig-
nificantly reducing the waiting time for agents.
CASE STUDY MALAYSIA – REGIONAL DIFFERENCES
Another parameter which is important, is regional differences within a country.
Taking Malaysia as an example: initially we provided landline sample as request-
ed by the client. During the project however it turned out that in some regions
landline numbers were working well, while in others it was almost impossible to
use landlines. What were the reasons for this?
After a thorough analysis, it turned out that within urban areas many landline
connections were in fact used for internet connections, and thus yielding a high
number of non-working numbers which could not be identified by pre-screen-
ing. sented areas is then enabled to ensure a representative geographical spread.
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7. Provider lookups
Furthermore in rural areas (were mobile communication was not fully estab-
lished), landline penetration was significantly higher. The last factor is that many
landline users within the rural areas actually abandoned the landline numbers
and thus further decreased the landline penetration, which further reduced the
amount the landline penetration in rural areas. In order to overcome these prob-
lems, it was decided to call on large scale with mobile phone numbers only
making use of a new technique called provider query lookup. This ensured a
high working rate of mobile phone numbers. Towards the end of a study when
quotas need to be filled, the landline sample for underrepresented areas is then
enabled to ensure a representative geographical spread.
MOBILE VERSUS LANDLINE SCREENING
Since RDD sample is randomly generated, there is always a large percentage
of dead numbers. Due to the different numbering block density, the fraction of
dead numbers varies. This is why the raw RDD sample is pulsed: in many Western
Countries, the filtering rate is between 30% and 50% (i.e. 30-50% of the num-
bers are screened out as non-working), thus leading to more effective landline
sample. However raw mobile phone pulsing only results in around 10% filtering
out of non-working numbers, this is why a provider lookup is used. The provider
lookup query indicates the following:
1. Is the SIM-card activated? 3. Is the phone switched on?
2. Is the number roaming? 4. Which provider is it?
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8. Summing up
This enables to call mobile phone numbers which have been active and switched
on within the last 24 hours, leading to more efficient mobile sample to dial on.
This is why in many South-East Asian countries, it is preferred to call mobile
sample rather than landline sample since the screening rate is a lot higher with
mobile numbers, compared to landline. Another factor is that the telephony
costs per minute are almost the same for landlines and mobiles, as opposed to
Western Europe.
Conclusion on Sampling
There are several conclusions that we can draw from this paper. It is important
to take several factors into account before targeting a population:
- Dialing costs (landline vs. mobile), especially for longer interviews
- Landline vs. Mobile penetration rate
- Regional differences
- Numbering block penetration
- Target population (age, gender etc.)
- Screening Effectiveness
Obviously not all these factors are evident straight from a simple lookup. How-
ever we are there to help you out with any questions you have.
For any questions or enquiries it is possible to contact us via info@samplesolu-
tions.eu or me directly via carsten.broich@samplesolutions.eu
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9. RDD LANDLINE SAMPLE
Efficient, Representative and Cost-Efficient
Random Digit Dialing, commonly known as RDD, is a very cost effective method for generating a
representative sample of households with fixed telephones. It is especially useful when No provision
for targeting within specific population groups is needed for example: Gender, income, geograph-
ical location or religion. Sample Solutions Europe has developed a highly accurate RDD procedure
while maintaining the representative proportion of the corresponding populations.
Some facts about our RDD Sample
Fastest turnaround:
Covering
30
>95 minutes, when using our
online ordering program.
countries worldwide
Up to
40
Sample variables
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10. RDD MOBILE SAMPLE
Do not miss the trend towards towards a mobile population
Our Mobile RDD sample is aligned with the provider share of each country, thus still providing a
representative spread of the target population. Furthermore it is possible via a provider lookup to
trach changes of the mobile provider. Our mobile RDD sample can be enriched with geodata using
a postcode linkage thus allowing geographic properties.
Facts about our mobile RDD sample
Listed RDD for
Mobiles are
3 months 65.000.000
Households wordwide,
ensuring perfectly targeted
cleared respondents.
Available in
95
Countries worldwide
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11. Get in touch !
Request some Trial Sample or ask for consultancy
At Sample Solutions we value long time relationships with our cleints. This is why we provide con-
sultancy on offline sampling and list features without any charge.
SAMPLE SOLUTIONS EUROPE offers access to more than 50 million business-to-business records
for market research and can deliver RDD sample for over 25 markets. Sample Solutions Europe was
established by a group of people with decades of experience in the (telephonic) research indus-
try. The lack of local sampling knowledge from the main players in the sample industry (for RDD
sampling), and the lack of details when providing B2B sample, led to the establishment of Sample
Solutions Europe.
We aim to provide better, and more detailed, sample, being it RDD or B2B, than any other
multi-market sample provider out there, at the best price-quality ratio possible. This philosophy has
lead to more and more clients from the international research industry finding their way to Sample
Solution Europe for their phone samples.
Contact: info@samplesolutions.eu
09

12. SAMPLE SOLUTIONS
Sample Solutions Europe
Groothandelsgebouw
3013 AP Rotterdam
Netherlands
Tel: +31 88 1267800
info@samplesolutions.eu