One of the most ubiquitous cognitive biases is overconfidence. As Daniel Kahneman writes:

The observation that '90% of drivers believe they are better than average' is a well-established psychological finding that has become part of the culture and it often comes up as a prime example of a more general above-average effect. (Thinking, Fast and Slow, p259-60)

However, this is not the only cognitive bias that arises when people are asked to estimate their position on a statistical distribution. A new paper by Daniel Sgroi and Eugenio Proto describes another one - that 'individuals tend to see themselves as more 'average" than is the case.":

Those at the extremes tend to perceive themselves as closer to the middle of the distribution than is the case. For example those who are left-wing see the population as more left-wing and feel themselves to be more typical, and those who own a particular type of mobile phone are likely to misperceive their own brand as more popular than is the case'taller and heavier individuals think that there are more tall and heavy individuals in the population.

This is not always a self-serving bias, nor is it the same as overconfidence; tall men, for example, would probably feel better about themselves if they had a more accurate image of their superior height.

The explanation for this might be straightforward. Likes tend to attract likes - lefties associate with lefties and lardies with lardies - and this, combined with the availability heuristic, leads people to over-estimate the extent to which others are like them.

I suspect this bias might have significant social significance. I can think of two ways, and there are probably more:

1. It leads to the 'middle England error' - the tendency of rich people to assume that their incomes are more typical than they really are. This can in turn cause the rich and influential to under-estimate the depth and breath of poverty.

2. Criminals often claim that 'everybody's doing it', perhaps because many of their friends are. In believing that behaviour is normal, though, they are more likely to do it. And so crime is higher than it otherwise would be.