The “timeline” method of studying electoral dynamics

To study the evolution of electoral preferences, Erikson and Wlezien (2012) propose assessing the correspondence between pre-election polls and the vote in a set of elections. That is, they treat poll data not as a set of time series but as a series of cross-sections—across elections—for each day of the election cycle. This “timeline” method does not provide complete information, but does reveal general patterns of electoral dynamics, and has been applied to elections in numerous countries. The application of the method involves a number of decisions that have not been explicitly addressed in previous research, however. There are three primary issues: (1) how best to assess the evolution of preferences; (2) how to deal with missing data; and (3) the consequences of sampling error. This paper considers each of these issues and provides answers. In the end, the analyses suggest that simpler approaches are better. It also may be that a more general strategy is possible, in which scholars could explicitly model the variation in poll-vote error across countries, elections, parties and time. We consider that direction for future research in the concluding section.