Ed Miliband delivered a speech this week in which he promised to cut the deficit if Labour wins the election in May. For many, this served as a reminder of the “deficit attention disorder” of the Labour leader, who ‘forgot’ to mention the deficit during his party conference speech in October. In this post, Jack Blumenau shows that, until now, avoiding talk of the deficit has been a systematic feature of Labour’s contribution to the political debate about the economy over the past four years. In a statistical analysis of parliamentary speeches, he shows that Conservative MPs are considerably more likely than Labour MPs to emphasise the deficit when debating economic issues. By contrast, Labour pays more attention to unemployment, austerity, and government cuts. One interpretation of these results is that Labour MPs strategically emphasise the issues on which the party holds a comparative advantage, and avoid issues which favour the Conservative party. Put in this context, Miliband’s recent speech marks a significant change in Labour’s long-term strategy, and suggests that Labour are willing to fight the election on issues that have previously tended to favour the Conservatives.

Which issues do politicians choose to emphasise when debating the economy? How do different actors emphasise different issues when discussing the same topic? One approach would be to select some words that we think are relevant to the topic at hand, and which might reveal partisan differences, and measure the frequency of their use between the two parties. For example, we could count the number of times that the two party leaders – Ed Miliband and David Cameron – use the word ‘deficit’ in their parliamentary speeches. By looking at all speeches made by the two leaders in the House of Commons between June 2010 and September 2014, this simple counting exercise reveals that the Conservative leader mentioned the deficit 520 times while the Labour leader mentioned it only 33 times. Although the raw difference is interesting, this simple counting method has a number of problems.

First, in any reasonably sized collection of texts, the number of unique words used will comfortably be in the thousands. For example, I use a corpus (a collection of texts) of all parliamentary speeches made by Labour and Conservative MPs since the last election: about a quarter of a million texts and over 15,000 unique words. Which of these thousands of words should we choose to analyse? Although we may be able to manually select an interesting subset, doing so might lead us to miss some of the most salient lexical differences between the two parties. It seems unlikely that we will always be able to guess, a priori, which are the best words to analyse.

Second, when confronted with such an avalanche of words (there are about one hundred and fifty million words in the corpus analysed here) it is difficult to know whether the simple differences in word use noted above are meaningful in either a statistical or substantive sense. For example, it might be that the raw counts for “deficit” presented above are simply due to the fact that the Cameron speaks more than Miliband.

Third, differences in word use might arise if the two parties devote different amounts of attention to different topics debated in parliament. Whilst this may also be of use in understanding political debate, it is not our direct interest here. Rather, our true interest lies in establishing whether Labour and the Conservatives adopt distinct rhetorical positions whilst discussing the same general topic.