Mozart's IQ: What the 1926 Stanford Study Actually Found

What the 1926 study found

Every serious figure for Mozart's IQ comes from one book. In 1926 Stanford University Press published Catharine Cox's The Early Mental Traits of Three Hundred Geniuses, the second volume of Lewis Terman's Genetic Studies of Genius. Cox took 301 eminent people born between 1450 and 1850 and asked what their IQs would have been had anyone tested them as children and young adults. Mozart, whose life and work are covered in our Mozart profile, was one of them.

Each subject received two ratings. For Mozart, the record from birth to 17 produced an IQ of 150; the record from 17 to 26 produced 155. Cox graded the evidence behind both at .75 on her reliability scale, a far firmer footing than the .43 she assigned to Bach's thin boyhood record.

These are ratio IQs. Cox defined the score as "the ratio of mental age to chronological age," judged against the childhood norms of the 1920s. They are not scores on the deviation scale used by modern Wechsler tests, and they carry no confidence interval of the kind a clinical report prints.

Three raters, a 65-point spread

Cox did not rate alone. Terman, the Stanford psychologist Maud Merrill and Cox herself scored all 301 subjects independently. On the young Mozart they split badly: Terman gave 125, Merrill 190, Cox 140. Cox wrote that the spread showed "the difficulty of estimating the intelligence of a musical prodigy."

Her case notes explain the problem. Mozart's family standing earned a starting guess of 115 to 120. His recorded interests were almost wholly musical. His reading and correspondence, she judged, showed no striking capacity. The imaginary kingdom he planned at 10 was merely corroborative, and his skill at cards and fencing added "nothing diagnostic." The case rested on music: a child playing keyboard at 3, composing at 5 and working through the most difficult counterpoint by 14.

The settled figure of 150 is therefore a negotiated number. It records how three psychologists chose to weigh extraordinary musical precocity against an otherwise ordinary paper trail.

Where the 165 comes from

Search for Mozart's IQ and 165 appears more often than 150 or 155. It is still Cox's number, adjusted. She found that her estimates rose with the quality of the evidence, so thin records produced low scores. To compensate she added a corrected estimate: "an approximation to the IQ that would have been obtained if the data had all been equally and sufficiently reliable." Secondary tables of those corrections list Mozart at 165.

The correction is a statistical projection, not new evidence about Mozart. It also flattens the field. The same tables put Beethoven and Bach at 165 as well, although their raw ratings sat 15 to 25 points below his. Quote 150 to 155 for Cox's actual judgment; treat 165 as her estimate of what better records might have shown.

The record behind the rating

Mozart's documented feats are specific and dated. He was composing at 5, with his father, Leopold, writing the pieces down. He wrote his first symphony at 8, during the family's London stay of 1764. On the Italian tour of 1769–1771 he heard Gregorio Allegri's Miserere twice in the Sistine Chapel and wrote it out from memory. His opera Mitridate, re di Ponto was staged in Milan in 1770, when he was 14.

The most unusual evidence came from a man of science. In 1764 the English lawyer and naturalist Daines Barrington examined the eight-year-old in London, asking him to improvise a "Song of Love" and then a "Song of Rage" fit for the opera stage. Barrington's "Account of a Very Remarkable Young Musician" appeared in the Royal Society's Philosophical Transactions in 1770. It is one of the earliest written assessments of a prodigy by an outside examiner.

The adult output confirms the childhood signal. Mozart wrote more than 800 works before his death at 35, among them Le nozze di Figaro (1786), Don Giovanni (1787) and Die Zauberflöte (1791). He left the Requiem unfinished.

The Mozart effect is a separate question

Many searches for Mozart's IQ are really about the Mozart effect. In 1993 Frances Rauscher, Gordon Shaw and Katherine Ky reported in Nature that 36 college students did better on spatial tasks, such as paper folding, after hearing Mozart's Sonata for Two Pianos in D major, K. 448. No student's gain outlasted the 15-minute testing window.

Later reviews shrank the finding. Christopher Chabris's 1999 meta-analysis judged the gain small and confined to one type of task, with no change in IQ or general reasoning. A 2010 meta-analysis by Jakob Pietschnig, Martin Voracek and Anton Formann, covering 39 studies, found little support for the effect and larger results in studies tied to the original lab. The idea still reached policy: in 1998 Georgia's governor, Zell Miller, proposed $105,000 a year to send classical-music recordings home with newborns. Rauscher herself said the research never claimed that listening to Mozart makes anyone smarter.

Mozart beside Beethoven and Bach

Within Cox's study Mozart sits at or near the top of the composers. The psychologist Dean Keith Simonton counted 11 classical composers in her sample and placed Mozart's estimate "between 150 and 155." Beethoven rated 135 and 140; Bach 125 and 140. Felix Mendelssohn received the same 150 and 155 as Mozart, and Handel came close at 145 and 155. Our composers ranked by estimated IQ sets out the full table, and the head-to-head pages Mozart vs. Beethoven and Mozart vs. Bach compare the work itself.

Simonton's own arithmetic cautions against reading the table as a leaderboard. Across those 11 composers, estimated IQ and eminence correlated at .54: a strong link, far from a decisive one. Beethoven, he wrote, may not have matched Mozart's intelligence, but he had "more than enough persistence to compensate."

What an IQ number cannot hold

Cox conceded the core difficulty in her own notes: Mozart's precocity, ability and mental development showed almost entirely in music. An IQ test samples reasoning, vocabulary, working memory and processing speed. It has no subtest for hearing a choral work twice and writing it out, or for sustaining invention across three decades of composition. That is why the raters split, and why any single figure for Mozart describes the method as much as the man.

For the wider prodigy question, see the history of child prodigies and what research says about music and intelligence.

How we assessed this

We read Cox's 1926 volume in its Internet Archive scan, including Mozart's case study and her discussion of the three raters, and checked the figures against Simonton's 2009 review in The Psychologist. We treat 150 to 155 as the estimate and 165 as a correction, and we use no figure without a named source. For the limits of retrospective scoring, see how historical IQ estimates work; for what 155 means on a modern scale, see IQ 155.

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.