In the U.S., the researchers had participants look at a screen showing a grid of 100 photographs with faces of Black people and white people in different proportions. Viewers had to estimate the overall percentages of Black and white people present after seeing a set of 20 such grids, each viewed for two seconds.

When 25 percent of the images in the grids were of Black people, white participants estimated the proportion of Black faces to be 43.22 percent, and Black participants put it at 43.36 percent. When 45 percent of the images were of Black faces, white participants estimated the proportion of Black people at 58.85 percent, and Black participants thought it was 56.18 percent.

In other experiments, participants were asked to estimate the proportions of Black and white faces directly after seeing each of a series of grids and to then make the same calculation after having gone through the entire set of 20 grids. In both cases, they overestimated the proportion of Black faces and underestimated the percentage of white faces.