For some years now, marketers have grappled with the challenge of how to explain 'brand love' – that intangible sense of attachment that makes Coke 'taste better' than Pepsi and may even lead us to overlook a product's shortcomings (think Apple). The 'roots' of brand love have generally been sought in the irrational, in emotions, yet this creates circularity: we love brands that create emotion; emotion creates loved brands, and so on…

Could it be, however, that the explanation lies in the relationship between our self and brands such that loved brands are those that somehow become subsumed in our personality? In other words, is a loved brand one that becomes part of us?

Over a century ago, William James argued that the self includes many things outside of one's self, including social relationships and material things. And, we know (from cognitive science) that, by entering into close relationships, individuals are able to subsume other people's identities into their self. The result is self-other overlap, where an individual's mental representations of his or her own self begin to merge with mental representations of a close relationship partner.

Since (close) others are included in the self and brands may act as relationship partners, it is surely reasonable to hypothesise that brands may also be subsumed in the self. Specifically, if a brand is loved or thought of as a 'close other' the mental representation of that brand should overlap with the psychological self.

My company has developed a new approach (Charismatix™) to measure the psychological overlap of brands with the people who love (and don't love) them. It uses a new metric called Self Brand Overlap™ (SBO) which quantifies the psychological distance between self and the perceived personality of a brand.

We first tested the hypothesis (that Self Brand Overlap™ predicts Brand Love) during the 2015 UK general election, measuring voters' personality overlap with the two main party leaders - Cameron and Miliband.

Despite neither candidate having strong appeal overall, it was clear that Miliband was less able to identify (i.e. overlap) with floating voters than Cameron. Indeed, there was a marked reluctance to identify with Miliband outside of his group of 'lovers'. By contrast, Cameron, despite being perceived as 'posher', was closer to the voters for being caring, sincere and even down to earth. Crucially Cameron almost matched voters' self-perception for honesty (-6) with Miliband trailing at -14.

This narrative is consistent with that put forward by some commentators: that Cameron won not because he is loved but because the alternative was worse. Is this 'personality gap' sufficient explanation for Cameron's victory? Maybe, maybe not, but it feels much closer to the mark than all the ineffectual waffling about 'shy Tories' and differential turnouts.

But does it work as well for brands? The short answer is 'yes', The method is already being tested with considerable success, revealing the hidden power of Self Brand Overlap™ as a predictor of brand love, and potentially handing marketers the code they need to re-engineer their brand's personality to reach out to the unconverted. In most categories relatively few customers identify strongly with the main brands: suggesting considerable potential for brands that reach out to those who neither love nor hate them (a point that Byron Sharp makes in How Brands Grow).