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Siegfried Gabler, Sabine Häder

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:

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Siegfried Gabler, Sabine Häder

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  1. Combining Landline Phone Samples and Mobile Phone Samples in Germany: a Dual Frame ApproachFirst Outcomes of a DFG*-Project Siegfried Gabler, Sabine Häder *DFG = Deutsche Forschungsgemeinschaft = German Research Foundation

  2. 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

  3. Quelle: http://www.bitkom.org/51940_50446.aspx Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008

  4. A challenge for survey methodology:The cell phone only households Source: Lepkowski et al 2008; own investigation Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008

  5. 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 1,009Cell phones 1,161 • Survey period October 2007-April 2008 Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008

  6. 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) Sampling procedure for cell phone numbers by BIK n ASCHPURWIS + BEHRENS GmbH *) Provider O2 allocates eight-digit numbers in connection with the prefix 0176. even though only seven-digit numbers were ordered at RegTP. Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008

  7. Dual frame survey Frame of landine phone numbers Frame of cell phone numbers person household person Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008

  8. Availability: cell phone usage Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008

  9. i = 1. ... . N (N is number of target persons in population Landline MFquantityofnumbers in frame mFquantityofnumbers in sample Selection: simple random sample Cell phone MCquantity of numbers in frame mCquantity of numbers in sample Selection: simple random sample 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

  10. 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). Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008

  11. Inclusion Probability Horvitz-Thompson-Estimator Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008

  12. ì 1 = F i.e. k í i 2.5 î Weighting model Problem: 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 Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008

  13. Availability: Quantity of cell phone numbers Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008

  14. Example DFG-Project Landline: MF = 129,725,800 mF = 16,154 Cell phone: MC = 178,050,000 mC = 23,955 n = 1,009 + 1,162= 2,171 Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008

  15. v4 = variable in data file Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008

  16. Histogram of weights 250 Cell phone Landline 200 150 Frequencies 100 50 0 0 2 4 6 8 weights Gabler/Häder, Landline/cell phone, Q2008 Rome 10 July 2008

  17. 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

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