Driven by data; ridden with liberty.
One of the assumptions underlying political populism is that if a party adopts a popular policy then the party itself will become popular.
David Miliband, the former South Shields MP who lost out in the 2010 Labour leadership contest to his brother Ed, was concerned about Labour’s “valence” in an interview . According to the Australian Times:
What matters, he said, is the party’s “valence” – a chemistry term meaning the attractiveness of an atom. “It’ about what are the composite qualities – credibility, trust, authenticity? – You don’t want to be the risk in politics, and you don’t want to be the risk if you are the opposition.
Valence politics is a term in political science, used to describe making judgments based upon image and identification with near-universal ideals .
For instance, nearly everyone wants healthcare that is of high quality, affordable and accessible. What matters is which party will come closest to achieving that ideal: who can do it, not necessarily needs to be done.
In the absence of detailed knowledge about the inner workings of healthcare systems, voters will use heuristics of party leader images and party identifications to determine who is most likely to ‘do the job’.
Note that this is a descriptive claim about politics: how it is in reality, rather than a normative claim of how we would like it to be.
This differs from a spatial view of politics, where voters choose the party that is proximate to their own beliefs. In the spatial model, policies and political positions may be placed on axes — either one or a small number — and the voter electorally supports the party with the minimal distance to themselves.
Despite its mathematical majesty, there are several criticisms of this explanation of voting, as identified by Donald E. Stokes .
The spatial model is theoretically flawed because it wholly relies on four key assumptions. Placing policies onto an axis presupposes that such an axis exists, that this issue is a political dimension voters think of; these axes are fixed, with parties moving like chess pieces; both political parties and voters recognise and agree what these political dimensions are; and political dimensions are totally ordered, meaning policies may be assigned numeric values where all policies are higher, lower or equal to all others.
It should be highlighted surveys that claim to tell you who you should vote for, based on policy preferences, are reliant on a spatial model of politics.
The problem is that politics is ever-shifting, ever-changing, with each new day bringing new challenges and questions. To this end, political parties persistently try to draw the lines of electoral choice to their own advantage.
Is it the choice between competence or chaos? Is it the choice between the stale status quo and a better plan for a better future? Is it the choice between political extremities or a centrist position? Is it the choice between hope and fear?
The populist prospectus — political parties can become popular by absorbing favourable policies — does not account for valence politics.
 Sylvester, R., and Savage, M., 2015. David Miliband: brother Ed’s British election defeat was doubly painful. Australian Times. Available from: http://www.theaustralian.com.au/news/world/david-miliband-brother-eds-british-election-defeat-was-doubly-painful/story-fnb64oi6-1227391975653 [Accessed: 3rd July 2015]
 Clarke, H. D, Sanders, D., Stewart, M. C., and Whiteley, P, 2011. Valence Politics and Electoral Choice in Britain, 2010. Journal of Elections, Public Opinion and Parties. Available from: http://www.bes2009-10.org/papers/electoralchoice2010.pdf [Accessed: 3rd July 2015]
 Stokes, D. E, 1963. Spatial Models of Party Competition. American Political Science Review, 57, pp 368-377.