Measuring Party Competition from Legislative Speeches: Analysis of Japanese Parliamentary Debates, 1953-2011

Among the existing measures of legislative behaviour, such as the use of roll call votes, this paper adds to the list by proposing a new measure of party competition by using legislative speeches. Legislative speeches have become increasingly accessible through digitalised databases in the recent years and we demonstrate how the use of legislative speeches can contribute to our understanding of inter-party and intra-party competition in the legislative arena. To this end, we propose a new measure of party competition which captures the level of confrontation between government and opposition parties. By implementing the latest technique of Wordfish (Sven-Oliver Proksch & Jonathan B. Slapin, 2009) to codify political texts, we extract an underlying dimension from legislative speeches that reflects the intensity of government and opposition divide. Through the database of the Japanese Diet, we codified speeches made by prime ministers and party representatives in the parliamentary sessions from 1953 to 2011 and extracted their positions in the scale of government and opposition divide. We demonstrate the use of this new measure by illustrating the change and dynamics of government and opposition divide and the ways in which parties’ behaviour is conditioned by electoral cycles. Our preliminary analyses indeed show that parties oppose to each other more intensely prior to elections but to a lesser extent in the middle of electoral cycles. The new measure also appears to account for other dimensions of legislative politics such as the survival rate of governments and the duration of time needed for governments to pass their proposed bills. While this measure could also be applied to the studies of coalition politics and of intra-party politics of factions, we hope to show some examples for an illustration of the measure and illuminate a possible venue in the future research on legislative politics.