Belief in our moral superiority is the most irrational self-enhancing bias of all

Most of us believe we are smarter, harder-working and better at driving than average. Clearly we can't all be right. When it comes to moral qualities, like honesty and trustworthiness, our sense of personal superiority is so inflated that even jailed criminals consider themselves to be more moral than law-abiding citizens.

Why should the "better-than-average" effect be so pronounced for moral traits? In new work, published in Social Psychological and Personality Science, Ben Tappin and Ryan McKay at Royal Holloway, University of London have found that it's because we're especially irrational when it comes to evaluating moral traits. Moral superiority appears to be "a uniquely strong and prevalent form of positive illusion," they write.

Tappin and McKay showed a list of 30 traits to 270 participants. Ten traits related to sociability (like being sociable, cooperative, rude or uptight); ten to agency (like being determined, creative, unmotivated or illogical) and ten to morality (like being principled, fair, manipulative or deceptive). They asked the participants to rate how much each trait applied to them and to the "average person", and to rate the desirability of the traits.

As expected, the participants gave themselves higher scores than they gave the "average person" for almost all the desirable traits (being sociable was a notable exception), and lower scores for the undesirable traits. They were, as the researchers expected, guilty of "self-enhancement".

But if you really are a particularly high or low scorer on certain traits, self-enhancement isn't necessarily irrational. We tend to be less certain about what other people are like, compared with ourselves, which means it sometimes makes sense to form less extreme judgements about their scores. As the researchers noted: "Perceived differences between ourselves and other people may even reflect rationally cautious judgements, made under uncertainty."

To explore to what extent the participants' self-enhancement was rational or irrational, Tappin and McKay factored in how typical their scores were, overall, compared with the average. For instance, if across the board an individual's personality is very average, and this shows up in most of their self-ratings, it looks a lot like irrational self-enhancement if on a given desirable trait they tend to inflate their own scores relative to the "average person". In contrast, for someone whose personality is overall more atypical, there's arguably more rational justification for them to infer that they are more extreme than average on various traits.

Following this logic, the researchers found that self-enhancement pertaining to sociability was mostly quite rational. Self-enhancement related to agency (being intelligent, determined and so on) was less rational. Least justified of all, or most irrational, was moral self-enhancement. "Virtually all individuals irrationally inflated their moral qualities, and the absolute and relative magnitude of this irrationality was greater than that in the other domains of positive self-evaluation," the researchers noted.

According to the prevailing theory of self-serving positive illusions, we hold inaccurate, overly rosy views of ourselves because they make us feel better about ourselves, and so boost our psychological wellbeing. Consistent with this, in the current study, greater irrational social and agency self-enhancement was correlated with having more self-esteem. Intriguingly, however, irrational moral superiority was not.

The study can't explain why we are most irrational when it comes to downplaying other people's moral qualities compared with our own, which was a surprise to the researchers. But there could be an evolutionary reason: from a survival perspective, the safe bet is to assume someone is less trustworthy than you, unless you know otherwise.

Future work could explore this. And, as the researchers also noted in their paper, it's important to dig into our inflated beliefs that we're just, virtuous and moral in part because these kinds of beliefs – in contrast to inflated ideas about our own determination, say, or cooperativeness – "likely contribute to the severity of human conflict. When opposing sides are convinced of their own righteousness," the researches noted, "escalation of violence is more probable, and the odds of resolution are ominously low".