A methodology is proposed for assessing the impact of televised debates on electoral outcomes, and it is applied to a specific case, that of the 1988 Canadian election. We present four tests of the debates' impact: first, a cross-sectional group comparison, which contrasts the voting behaviour of those who did and those who did not see the debates; secondly, a panel analysis of the shift in party support, before and after the debates, among those who watched the debates and those who did not; thirdly, a panel study of the impact of reactions to the debates on voting behaviour; and, fourthly, a time-series analysis, which examines the evolution of vote intentions over the course of the campaign and, more precisely, before and after the debates.
It is argued that because non-watchers are influenced by what their friends or the media tell them about the debates, the first two designs, based on a comparison of debate watchers and non-watchers, are not appropriate. The empirical analysis of the 1988 Canadian election substantiates this point. While these first two designs seem to indicate no debate impact, panel reaction and time-series analyses show that the debates had a substantial and enduring impact on the vote and that they were decisive in the contest for second place between the Liberals and the NDP.