Consider an experiment in 2003 by Marianne Bertrand and Sendhil Mullainathan, two American economists. They drafted 5,000 CVs and placed archetypal “black” names such as Tyrone or Latoya on half of them and “white” names such as Brendan or Alison on the other half. They then divided the white CVs into high and low quality and did the same with the black CVs.

A few weeks later the offers came rolling in from employers, and guess what? The “black” candidates were 50% less likely to be invited to interview. Employers were using skin colour as a marker for employment potential, despite the fact that the candidates’ CVs were identical.

But that’s not all. The researchers also found that although high-quality “white” candidates were preferred to low-quality “white” candidates, the relative quality of “black” CVs made no difference whatsoever.

It was as if employers saw three categories - high-quality white, low-quality white and black candidates. To put it another way, the subliminal assumption that causes us to think that black people are all the same has powerful real-world consequences.