Ian Budge and Michael D. McDonald, "Choices Parties Define: Policy Alternatives in Representative Elections, 17 Countries 1945-1998" Party Politics, 12 (July, 2006), 451-466.

First Paragraph:
Recently, a new and detailed source of information on the policies electors vote on has become available in the shape of coded party manifestos (platforms) for a variety of countries in the post-war period (Budge et al., 2001). In many ways, this information is as important for understanding the nature of modern elections as voting surveys. Votes, after all, have to be cast so as to favour particular parties and their programmes. Insofar as election results influence the type of public policy to be pursued, this can be done only in terms of the policies parties offer as alternatives at the current election. Over time, of course, parties and policy alternatives may change. The remarkable stability of most party systems over the post-war period suggests, however, that really radical change rarely occurs (cf. Figures 1-4). Parties stick to fairly consistent policy lines over time. Nevertheless, within ideological limits they do move (cf. Figures 1-3). This suggests that it is worthwhile estimating the policy positions they actually take rather than just assuming them from the ideological leanings of the party - even though, inevitably, we are forced for some purposes to summarize the evidence by presenting mean post-war positions for most countries and parties. We try to get behind the aggregate figures, however, by investigating what these signify in terms of the underlying policy packages offered to electors on key issues (Table 3).

Figures and Tables:
Table 1. Scoring a Left-Right scale on the basis of the manifesto estimates
Figure 1. United States party movements on a Left-Right scale, 1952-96
Figure 2. United Kingdom party movements on a Left-Right scale, 1950-97
Figure 3. French party movements on a Left-Right scale, 1951-97
Figure 4. Distinctiveness of choices offered by parties along the Left-Right dimension, by country over post-war period
Table 2. Scoring party positions on welfare, military and market policy on the basis of the manifesto estimates
Table 3. Policy packages offered by major parties in 17 post-war democracies

Last Paragraph:
It is worthwhile to look at general tendencies in the choices that have faced electors over the series of post-war elections. This we have done by locating average positions for all parties in Left-Right terms (Figure 4) and analysing the nature of the specific policy alternatives the major parties normally combine into a package and place before the electorate (Table 3). We have concluded that these do offer real policy alternatives to electors, which are more or less polarized (and conversely more or less overlapping) in different countries, not so much because of different institutional arrangements like PR and a multiparty system, or SMD and limited parties, but because of parties' strategic and policy choices in the past. These are probably bound up with national history and the country's geographic location rather than more narrowly defined institutional factors. In the end, electors can vote for no more than what the parties offer. Parties structure the electoral debate and define the alternatives being voted on. What we have shown here is that they do, in general, offer meaningful alternatives, which electors can vote for to send a reasonably clear message to the political elite about how public policy should be adapted to their preferences.