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 …