Psychologist Lewis Terman pioneered a historiometric approach to IQ assessment, in which the IQ of a historical figure is estimated from biographical data with an emphasis on childhood precocity. So while reading a biography of mental testing pioneer Sir Francis Galton, Terman noted that between the ages of three and eight, Galton was intellectually functioning at twice his chronological age, and thus assigned him an astonishing ratio IQ of 200 since Galton’s cognitive development was progressing at 200% of the normal rate.

Terman’s analysis of Galton would lead to the Cox study in which the IQ’s of about 300 historical figures were estimated from reading their biographies, and more recently, there was an interesting historiometric attempt to estimate the IQ of horror author H.P. Lovecraft.

In a biography of Oprah called Oprah Winfrey: The Real Story by journalist George Mair (pg 8), it’s reported that Oprah’s grandmother taught her to read, write and do arithmetic by the time she was three. Also at the age of three, Oprah stood before the church congregation and said:

Jesus rose on Easter Day. Halelu, halelu, all the angels did proclaim!

Based on her ability to learn and recite, it sounds like Oprah at the age of three was functioning verbally at the level of a five or six year old. Based on this I would assign her a Verbal ratio IQ of 183 since her verbal skills were developing at 183% of the normal rate.

Now in this video, Oprah interviews her fourth grade teacher. Oprah claims that in the fourth grade, she found long division difficult, however her teacher doesn’t recall Oprah struggling with anything and claims she grasped concepts readily. The truth is probably somewhere in between, so let’s assume Oprah learned long division as quickly as the average fourth grader. However Oprah skipped Kindergarten and second grade so she was younger than her classmates, though only one year younger because she was born in January. So while most kids are learning 4th grade math (long division) at age nine, Oprah was learning it at age eight. This means her math skills were developing at 113% the normal rate which gives her a math ratio IQ of 113.

Averaging her Verbal ratio IQ of 183 with her Math ratio IQ of 113 gives an overall ratio IQ of 148, or roughly 150. According to scholar Vernon Sare, one in 286 children had ratio IQ’s this high or higher (the top 0.3%).

On modern IQ scales (known as deviation IQ scales), scores are forced to fit a normal curve with a mean of 100 and an SD (standard deviation) of usually 15, which means the top 0.3% equates to an IQ of 141. So Oprah would have a deviation IQ of about 140, which is precisely what one should statistically expect for someone of her background, brain size, and success level.

Of course, an extremely high childhood IQ does not always turn into an extremely high adult IQ. However new research shows that when childhood IQ is measured accurately, it’s actually far more predictive of adult IQ than traditionally thought.

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