In a sequential mixed mode survey, instead of offering different modes from the onset, the
data collection usually starts with an inexpensive mode for the whole sample, followed by more expensive
modes to attract non-respondents. In this paper, we analyze to what extent this type of design, consisting
in this case of web, telephone and mail-paper modes, is able to improve representativeness in terms of
socio-demographic variables and reduce bias in terms of voting behavior compared to a single mode
survey. In addition, we study whether changes in mode lead to measurement error issues by focusing on
income. We find that adding the telephone mode improves sample representation in terms of sociodemographic
variables, while adding the paper mode does not show further improvements in this respect.
However, adding the telephone, and in particular the paper mode, turn out to reduce bias in terms of
voting behavior. As for measuring income, the web and the telephone mode perform similarly well.
Finally, we find little evidence of measurement differences of income when the same respondents are
interviewed first by web or telephone and subsequently by paper questionnaire.