According to this source, 50% of American adults can’t read an 8th grade book.  Since the 50th percentile of American IQ is average IQ; about 100 (U.S. norms; 97 U.S. white norms), then on the IQ scale, 8th grade reading level = IQ 100 (97 on U.S.white norms).

More than 20% of U.S. adults read below the fifth grade level.

Since the 20th percentile of Americans is IQ 88 (U.S. norms; 84 on white norms), then on the IQ scale, 5th grade reading level = IQ 88 (84 on white norms).

From here, we can make simple linear formulas converting reading levels to IQ equivalents:

U.S. norms:

IQ  = 68+4(reading level)

U.S. white norms:

IQ = 62.333+4.333(reading level)

The tragic death of boxer Muhammad Ali has inspired much commentary, including from iconic blogger Steve Sailer and National merit finalist ruhkukah who recently said on this blog:

Muhammad Ali, who just passed away, may be one of the best examples of the failure of IQ to capture every aspect of human mental ability. He was one of the most charismatic men of his time, known for his unique verbal facility, in addition to being a great boxer and athlete.

Ali’s actual IQ score: 85 not 78

For decades it’s been reported that Muhammad Ali scored the equivalent of 78 on army testing (I first saw the figure in Daniel Seligman’s 1992 book A Question of Intelligence), but upon doing a bit of research, I realize that everyone has been wrong.  Ali scored at the 16th percentile on the test, which for whatever reason, sources are equating with an IQ of 78, but on a standard scale with a mean of 100 and a standard deviation of 15, the 16th percentile of Americans is actually IQ 85. Someone clearly made a clerical error, and it got repeated over and over and over again. No one bothered to fact check, until now.

Of course these norms include non-whites which tends to inflate them relative to the traditional white normed IQ scale.  On the other hand they exclude women, which deflates the norms.  Since the inclusion of non-whites negates the exclusion of women, Ali likely scored 85 on sex-combined white norms (the traditional IQ scale and the international IQ scale).

However ruhkukah’s point still stands.  Even an IQ of 85 sounds very low for a man as impressive as Ali, but we have to put in perspective.

Average IQ of the subculture boxers are recruited from? About 74

Boxers are generally drawn from the most violent segment of the black underclass, since their job is essentially sanctioned assault.  Thus the population Ali must be compared to is the black incarcerated population, a sample of which had a mean IQ of 78.47 (SD = 8.24) (U.S. norms) on the WAIS-R.  After adjusting for inflated norms (the study was published in 1987 and the WAIS-R was normed in 1978), this becomes a mean IQ of 75.77 (SD = 8.24).  But because the WAIS-R norming included non-whites, the white mean was driven up to 101.4 and the white SD was driven down to 14.65.  Converting to white norms (the traditional standard), where the white mean and SD by definition are 100 and 15 respectively, the black inmates now have a mean of 74 and an SD of 8.44.

Statistically expected IQ of the greatest boxer of his generation: About 85

Americans like Ali, born from 1925 to 1942 are the “Silent Generation” and there were 20 million of them.  Of these, 1.2 million were black males, and of those, given that in the 20th century, about 29% of U.S. black males ended up in jail during their lives, perhaps 348,000 of these 1.2 million black males were part of the tough subculture from which boxers are recruited.

Assuming Ali was the best fighter in this group, he’d be 4.53 SD above them in boxing performance and given the 0.8 correlation between performance and “raw talent”, we’d expect Ali to be 0.8(+4.53 SD) = +3.62 SD above this group in raw kinesthetic ability.

Given the 0.35 correlation between IQ and physical coordination found by the U.S. Department of Labour cited in Seligman’s 1992 book, we’d expect Ali’s IQ to be 0.35(+3.62 SD) = +1.27 SD above his ethno-social class.

This is probably an overestimate given that correlations tend to be smaller in homogenous subgroups.

Nonetheless, the prediction hits the mark. If the black male gangster class has a mean IQ of 74 with an SD of 8.44, Ali’s expected IQ would be 1.27(8.44) + 74 = 85 which is exactly how he scored on the Army intelligence test!

IQ isn’t everything

Some might question how someone so verbally quick and charismatic, not to mention iconic and influential, could have had an IQ of “only” 85, but I actually think the low IQ was part of his charm because it gave him a childlike innocence and enthusiasm that the public found endearing.  But for all his gifts, in the end Ali struggled to adapt the situation to his advantage (the ultimate test of intelligence). His promoters got rich at the expense of his health, while the final decades of Ali’s life were tragic.

Nonetheless he will go down in history as one of the most admired people of the 20th century for his athletic gifts, creativity (he’s been called the first rapper), stage presence, moral courage in opposing the Vietnam war, and the pride, dignity, and status he brought to his people.  He will be deeply missed.