combining landline phone samples and mobile phone samples in germany: a dual frame approach first...
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Combining Landline Phone Samples and Mobile Phone Samples in Germany: a Dual Frame Approach First Outcomes of a DFG*-Project. Siegfried Gabler, Sabine Häder. * DFG = Deutsche Forschungsgemeinschaft = German Research Foundation. Overview. The main problem: - PowerPoint PPT PresentationTRANSCRIPT
Combining Landline Phone Samples and Mobile Phone Samples in Germany:
a Dual Frame Approach
First Outcomes of a DFG*-Project
Siegfried Gabler, Sabine Häder
*DFG = Deutsche Forschungsgemeinschaft = German Research Foundation
Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008
Overview
• The main problem: The cell phone only households
• Description of the DFG-Project
• First results: - sampling procedure - weighting
Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008
Quelle: http://www.bitkom.org/51940_50446.aspx
Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008
A challenge for survey methodology:The cell phone only households
Slovakia 2008 55%
Finland End of 2006 52%
Poland 2007 24%
France 2006 17%
UK 2006 10%
Germany 2007 8%
Source: Lepkowski et al 2008; own investigation
Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008
DFG-Project: Interviews via cell phones• Cooperation TU Dresden and GESIS-ZUMA• Two parallel surveys: one via landline, one via cell
phone• Aims of the project:
- Investigation of mode effects- Response behaviour- Weighting model for the combination of both samples
• Respectively ca. 1,000 people interviewed Realization: Landline 1,009 Cell phones 1,161
• Survey period October 2007-April 2008
Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008
Sampling procedure for cell phone numbers by BIK ASCHPURWIS + BEHRENS GmbH
All hypothetical numbers assigned:279,000,000 numbers*
Generated numbers on basis of used number blocks :
178,050,000 numbers
Registered numbers2,297,460
(January 2008)
*) Provider O2 allocates eight-digit numbers in connection with the prefix 0176. even thoughonly seven-digit numbers were ordered at RegTP.
Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008
Dual frame survey
Frame of landine phone numbers Frame of cell phone numbers
household
person
person
Landline Cell phone
n % n %
Exclusive use by myself
790 91.1 1051
90.6
Other people use it from time to time
57 6.6 96 8.3
Share it with others 20 2.3 13 1.1
∑ 867 100.0 1160 100.0
Availability: cell phone usage
Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008
Landline MF quantity of numbers in frame mF quantity of numbers in sample Selection: simple random
sample
Cell phone MC quantity of numbers in frame mC quantity of numbers in sample Selection: simple random
sample
i = 1. ... . N (N is number of target persons in population
kiC Quantity of cell phone numbers allowing access
to person i.
kiF Quantity of landline numbers allowing access to
the household to which person i belongs. Selection: Kish table/last birthday
zi Size of household to which person i belongs.
Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008
Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008
Weigthing model: basic assumption
The probability of choosing two (not necessarily different)
members of the same household via different modes is insignificant.
(Could be a problem in small regional samples).
Inclusion Probability
1 , 1,...,F C
F Ci i iF C
i
m mk k i NM z M
( 1) 1 1 1 1 ( 1)( 1) ( 1)
1 1 1 1
F F F C F C C CF F F C C F C C
ij i j i j i j i jF F F C F C C Ci j i j
F F F C F C CF F F C F C Ci j i j j i iF F F C F C C
i j i j
m m m m m m m mk k k k k k k kM M z z M M z M M z M M
m m m m m m mk k k k k k kM M z z M M z M M z M
CCj C
i j
mkM
Horvitz-Thompson-Estimator
0
11 1Fi
F F Fi i
j FkFi F
j iF
k M kj m j
z Mm
1 1 1F C F C F Ci i i i i i i
1
C Ci
CCi C
C
M km
Mm
Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008
Weighting modelProblem: Most of the household members do not know the exact quantity of
landline numbers allowing access to their household.
Therefore the simplified assumption:
Landline (analog): 1 number
Landline (ISDN): 2.5 numbersISDN = integrated services digital network
1i.e.
2.5
Fik
Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008
Availability: Quantity of cell phone numbers
Landline Cell phone
n % n %
One 771 88.82 915 78.74
Two 71 8.18 192 16.52
Three 19 2.19 34 2.93
Four 3 0.35 9 0.78
Five and more
4 0.46 12 1.03
∑ 868 100.0 1,162 100.0
missings 141 0
Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008
Example DFG-Project
1.08F C
F C
M mm M
Landline: MF = 129,725,800
mF = 16,154
1 , 1,...,F C
F Ci i iF C
i
m mk k i NM z M
Cell phone: MC = 178,050,000
mC = 23,955
n = 1,009 + 1,162 = 2,171
in sample in sample
1
1 11.081.08
i
i FCii F
j j j j Cij
j
nw nk k
kzk
z
Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008
Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008
v4 = variable in data file
Histogram of weights
weights
Freq
uenc
ies
0 2 4 6 8
0
50
100
150
200
250
Cell phoneLandline
Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008
Following Steps
• Evaluation• Publication of the results in Häder. M. und Häder. S.
(Hrsg.): Telefonbefragungen über das Mobilfunknetz. VS Verlag. Winter 2008.
• Consecutive application for the DFG: calculation of the response rates
• Conference in Mannheim about the results of the DFG-Project. November 14th. 2008
• Further project within the framework of the DFG-program „Survey Methodology“: Mobilpanel together with Marek Fuchs (University of Kassel)
Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008