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184 FRIDAY 22 JULYIn order to invesgate the advantage of mixed-mode surveys, selecon effects between the modes should beevaluated. Selecon effects refer to differences in respondent composions on the target variables betweenthe modes. However, esmaon of selecon effects is not an easy task because they may be completelyconfounded with measurement effects between the modes (differences in measurement error). Publicaonsconcerning the esmaon of these mode effects are scarce. This paper provides and compares three methodsthat enable evaluang measurement effects and selecon effects separately. The first method starts from exisngpublicaons where the confounding problem is usually avoided by introducing a set of mode-insensivevariables into the analysis model. However, this paper will show that this method precludes exact esmaonof the effects...4.14.3 Tesng between-mode measurement invariance under controlled selecvity condionsT. Klausch 11 Utrecht University, NetherlandsAs more survey modes have become available, it has ever been an aspiraon in survey methodology researchto test and assure comparability of measurements obtained in different modes. Such research has oen found’mode effects’, which are measurement differenals between modes beyond sampling variaon. Moreover,with the rise of the mixed-mode survey, which combines more than one survey mode in the data collecondesign , the queson of comparability has become even more pressuring.4.14.4 Separang selecon from mode effects when switching from single (CATI) to mixed mode design(CATI / Web) in a health surveyJ. Carstensen 1 , P. Kriwy 1 , G. Krug 3 , C. Lange 21 University of Erlangen-Nuremberg, Germany; 2 Robert Koch Instute, Germany; 3 Instute for EmploymentResearch, GermanyAsking sensive quesons in surveys is prone to mode effects. To analyze the consequences of switching fromsingle to mixed mode designs, we randomly assign survey parcipants to a single mode (CATI) and a mixedmode (CATI and Web-based) survey. Both surveys contain the same set of items based on already establishedinstruments from German health surveys conducted by the Robert Koch Instute. The instruments cover sensiveitems such as subjecve well-being, health behavior and self-reported illness, augmented with quesonsabout confidenality concerns. Because of randomizaon differences in means are informave on the net impactof switching to mixed mode. Applying a Blinder/Oaxaca decomposion method from econometrics to thefield of survey methodology, we are able to separate (1) selecon effects due to differences in non responserates from (2) mode effects due to differences in item non response and measurement error...4.15 Potenals and constraints of weighng to improve survey quality ITo be held on July 22, 2011 from: 11:00 to 12:30, in room 303.Coordinated by:• Stephanie Steinmetz - University of Amsterdam, Netherlands• Kea Tijdens - Erasmus University, Netherlands4.15.1 Propensity Score Weighng: Methods and ApplicaonsM. Bergmann 11 University of Mannheim, GermanyDespite the increasing use of online surveys in polical opinion research, the field sll lacks thorough researchmapping the effects of this polling tool on achieving representaveness. For cause, the two most salient problemsassociated with online research – limited internet coverage and selecvity of respondents – have not yet