If IQ were skin color, how visible would the racial gap be?

I often describe the differences between groups in terms of standard deviations or Cohen's d, but maybe we can get a clearer picture of what these mean with a black-and-white example; namely, skin tone.

Skin color is a very noticeable racial difference and tends to dominate discussions of race even though it is just one characteristic. People focus on it because it is obvious, and I suspect race deniers like it because they can treat it as something superficial, something only shallow people would focus on. People like Dinesh D'Souza who I often agree with will say idiotic things like race is nothing but a "coat of paint." Never mind that skin is our largest organ and carries out many important functions, and that skin color appears to have important functions as well. And anyone who claims that aesthetics aren't important doesn't know human nature.

Anyway, General Social Survey interviewers were asked to rate the skin tone of respondents with a number ranging from 1 (lightest) to 10 (darkest). The lightest ethnic group is Americans of Danish descent with a mean of 1.33. (I'm weird because I'm all NW European and 1/8th Danish but look like an Arab). We'll use Danes as the comparison group. What I show below is the gap between the Danish mean and the mean for the focal group in terms of standard deviations:

Degree to which group is darker than Danish Americans (in sd units)

Blacks  2.2
West Indians  2.2
Asian Indians  1.3
Mexicans  0.8
Filipinos  0.8
American Indians  0.8
Puerto Ricans  0.7
Chinese   0.6
Japanese   0.6

Total Sample  0.6

Spanish   0.5
Arabs   0.5
Jews  0.3
Portuguese  0.2
Italians  0.2
Greeks  0.2

A gap of 2.2 standard deviations between Danes and blacks is so huge, it's the reason why people decided long ago to define groups as the opposite of each other: black and white. If a study reports a 2 sd gap, be impressed.

Another way of describing the gap goes like this: not a single black in the sample is lighter-skinned than any Dane, and 97% of Danes are lighter than 94.5% of blacks.

If you want a visual that matches the size of the black/white IQ gap (1 sd), think of the color gap between Danes and a typical Mexican and typical Asian Indian blended together--a very large difference. Another way of saying this is that the black/white IQ gap is only half the size of the color gap.

Even a difference that is only 10% of the black/Dane gap is still visually easy to detect: the Italian and Greek means are 0.2 standard deviations darker than Danes--0.2 considered a very small difference--but southern Europeans are known for being darker than northern Europeans. The higher Spanish mean is probably due to darker Hispanics claiming Spain as their homeland.