The association fallacy is an automatic short cut we all take from time to time. It’s why companies spend fortunes to be linked with popular celebrities and drop like a stone those whose actions might impinge on carefully crafted brand values. In many cases there’s no logic to the way we feel. Just because a certain person has particular characteristics or views it doesn’t follow they are shared by his colleague or imbued by his aftershave. But despite its logical shortcomings, the association fallacy is deeply ingrained and potentially damaging. A study by social scientist Michelle Hebl, for example, showed how the same job applicant was viewed less positively when seen sitting next to an overweight person than when sitting next to someone slimmer.

Guilt and honour by association are part and parcel of political life and something that both Ed Miliband and David Cameron have been grappling with of late. In Miliband’s case, the roles of Harriet Harman, Jack Dromey and Patricia Hewitt at the National Council for Civil Liberties in the 1970s have associated their party with the Paedophile Information Exchange. There has been plenty of media analysis about who said what and when. But whatever really happened at the time, the association has been made. And the longer it has been allowed to go on, the deeper the association has become.

The Conservatives then found themselves hit with a problem of their own. David Cameron’s aide Patrick Rock has quit his Number 10 position and been arrested over allegations connected with child-abuse imagery.

Far less shocking, but perhaps equally damaging in a political sense, a YouGov poll for the Times yesterday showed that 38% of people think going to Eton makes a person unsuitable as a leading politician. It’s apparently worse baggage than taking heroin or youthful shoplifting, though not as bad as never having had a proper job.

It’s hard to tell whether this has any tangible political impact. But unflattering associations undoubtedly pile up on top of one another to crowd out the detail of any given issue. In this toxic environment, there is a sense that all politicians are guilty by association with other politicians – even those with whom they vehemently disagree. Policies and messages then count for little if the natural conclusion for many voters is already “a pox on both their houses”.

Image of No 10 Downing Street courtesy of pcruciatti / Shutterstock