Kim Peek's IQ: Why an 87 Could Not Measure the Real Rain Man

The score on record: 87, with a canyon inside it

Kim Peek sat a standard intelligence test in 1988, the year Rain Man reached theaters. His full-scale IQ came back at 87. Psychiatrists Darold Treffert and Daniel Christensen, who studied him for years, reported the result in Scientific American in December 2005 and added that his verbal and performance subtests "varied greatly." Some landed in the superior range. Others fell in the range then labeled mental retardation.

On the Wechsler classification, 87 is low average, near the 19th percentile: higher than about 19 of every 100 people. It is the only measured IQ on record for Peek, and it is the number people find when they search his name. His life and work are covered on his genius profile; this page deals with what the number means.

It means less than it appears to. A full-scale IQ is an average of subtests. When those subtests agree, the average describes the person well. When they stretch from superior to impaired, as Peek's did, the composite describes no one. It flattens a peak and a valley into a plain.

A memory with no recorded equal

Peek read a page in eight to ten seconds, according to Treffert and Christensen, and kept what he read. By 2005 they counted about 9,000 books committed to memory. By his death in 2009, the Deseret News put the total above 12,000, including the Bible and the Book of Mormon in their entirety.

He read an open book two pages at a time, the left page with his left eye and the right page with his right. His knowledge ran across roughly 15 domains, among them world and American history, geography, sports, film, the space program, Shakespeare, the Bible and classical music. He knew the area codes and zip codes of the United States and the television stations that served them. He could name hundreds of classical works on hearing them and say when and where each was composed. Told a stranger's birth date, he could give the weekday and the front-page news of that day.

"He had a bottomless memory," Christensen told NPR after Peek died.

Where the same mind struggled

The gap ran the other way just as sharply. Peek could not explain many commonplace proverbs, Treffert and Christensen wrote, and had "great difficulties with abstraction." He walked with a sidelong gait, could not button his clothes and needed help with the chores of daily life. He did not walk until he was four.

That split explains the 87. Standard IQ batteries mix tasks that reward stored knowledge with tasks that demand abstraction, flexible reasoning and speed on unfamiliar problems. A profile like Peek's, encyclopedic recall beside weak abstraction, is exactly the kind that pulls such a battery apart, and the arithmetic mean lands near the middle. The test did its job. It estimated general reasoning, and Peek's gift was not general. For how modern batteries are built, see how IQ tests work.

An unusual brain, scanned by NASA

Peek was born in Salt Lake City on November 11, 1951, with an enlarged head and a damaged cerebellum. He had no corpus callosum, the thick band of fibers that links the brain's two hemispheres, and smaller connecting pathways such as the anterior commissure were also missing. In 2004 scientists at NASA's Ames Research Center examined him with CT and MRI scans to build three-dimensional views of his brain and compare them with scans made in 1988.

Doctors first described him as autistic. A 2008 genetic study proposed instead that he had FG syndrome, a rare X-linked condition. No one has shown how his anatomy produced his recall. When he died, Scientific American noted that the role of the missing corpus callosum in his abilities remained unclear. That is still the honest position.

From a chance meeting to four Oscars

Screenwriter Barry Morrow met Peek by chance in 1984 in Arlington, Texas. Morrow built the character of Raymond Babbitt partly on Peek and partly on Bill Sackter. Rain Man opened on December 16, 1988, with Dustin Hoffman as Raymond, and won four Academy Awards: best picture, director, actor and original screenplay, the last shared by Morrow and Ronald Bass. Hoffman met Peek while preparing the role. Morrow later gave Peek his Oscar statuette, which was passed from hand to hand at Peek's public appearances.

Treffert and Christensen called the film a turning point in Peek's life. He and his father, Fran, who cared for him alone after his parents divorced, became traveling advocates for people with disabilities. By 2005, the researchers wrote, the pair had shared their story with more than 2.6 million people. In his later years Peek also took up the piano. He died of a heart attack at his home in Murray, Utah, on December 19, 2009. He was 58.

Peek beside other extraordinary minds

Peek belonged to a small group. Researchers estimate that between 0.5 and 10 percent of autistic people show some savant ability, and that fewer than 100 living savants have skills that would be spectacular even among people without any disability. Peek was the most famous member of that top tier. The Deseret News headline on his death called him a "mega-savant."

Set beside other savants, his distinction was breadth. Daniel Tammet recited pi to 22,514 digits in 2004, a feat in one domain; Peek held about fifteen. Our comparisons of Peek and Tammet and of Peek and Stephen Wiltshire set the skills side by side.

Set beside prodigies known for towering reported scores, he is their mirror image. The famous figures for William James Sidis and Michael Kearney rest on unverified accounts. Peek's number is documented and modest; his ability is what defies measurement. An 87 sits eight points below the score discussed on our IQ 95 page, well inside the ordinary range of human scores.

What the number leaves out

An IQ test estimates general reasoning ability against a population norm. It was never designed to capture a memory that held thousands of books nearly word for word. Peek scored in the ordinary range on the instrument and far outside every range on the skill the instrument ignores. Both facts are true at once.

That is why the question of whether he was a genius has two honest answers. By IQ, no: 87 is below average. By achievement in one domain, his recall has no documented equal. "I don't think there has been anyone like Kim in recorded history," Christensen told NPR. Howard Gardner cited savants as evidence for his theory of multiple intelligences, and Peek is the clearest case: a mind whose strengths refuse to average out.

How we assessed this

We treated Treffert and Christensen's account as the primary source for the 1988 score, because they examined Peek directly and published under their own names. The original test report is not public, so the exact battery and index scores are unknown, and we do not guess at them. Book counts come from researchers and from obituaries; they are estimates, not audits. Dates come from contemporary news coverage. For how measured scores differ from retrospective ones, see how historical IQ estimates work.

Editorial standard: IQ figures for historical figures are retrospective estimates and are labeled as such; scores for living people appear only when the person disclosed them or a reputable outlet reported them. Corrections: contact the editors.