Mode-switch protocols: How a seemingly small design difference can affect attrition rates and attrition bias

We consider the effect of a wave of mixed-mode data collection (telephone and face-to-face), in an otherwise face-to-face survey, on panel attrition and the extent to which this effect is dependent on the nature of the mode-switch protocol. Findings are reported from an experiment on a survey in which the objective is to interview each adult member of the household. One protocol involves making extended efforts to interview each household member by telephone before switching to face-to-face, while the other involves switching a household to face-to-face as soon as it is apparent that an interviewer visit will be needed for at least one household member. With both protocols response rate at the mixed-mode wave is lower than with face-to-face single mode data collection, but with the protocol involving extended efforts this response differential is eroded over the following two waves, while with the other protocol the difference remains.