The Truth About IQ

By David Shenk

"[Some] assert than an individual's intelligence is a fixed quantity which cannot be increased. We must protest and react against this brutal pessimism."
         - Alfred Binet, inventor of the original IQ test, 1909


Last week, I argued that our 21st century understanding of genetics invalidates the idea of fixed, innate abilities. Genes influence everything but determine almost nothing on their own. 

What, then, is IQ? Conventional wisdom says that IQ scores reveal our native intelligence. According to this view, IQ tests are different from school grades, different from SAT scores, different from any other test you will ever take, because they somehow reveal the core, innate abilities of each person's brain: your clock speed, your RAM, your absolute limit. 

That's what Stanford psychologist Lewis Terman wanted us to believe when he introduced the American version of the IQ test in 1916. (This was quite the opposite intention of the test's original co-inventor, Alfred Binet. But that's a history lesson we'll return to another time.)

What Terman had actually come up was a deceptively simple system for ranking academic progress. His Stanford-Binet tests measured many different skills, and then scored the results so that the median was always 100. If you had an IQ score of 100, it simply meant that half of the test-takers your age had done better and half had done worse.

These tests were impressively stable, which meant that, over time, most people ended up in roughly the same place in the pack. If you had tested in the 60th percentile at age 10, chances were pretty good that that you'd test close to the 60th percentile at age 12 and age 14. 

But did this stability prove that the tests revealed innate intelligence?

Far from it. The reality is that students performing at the top of the class in 4th grade tend to be the same students performing at the top of the class in 12th grade, due to many factors that tend to remain stable in students' lives: family, lifestyle, resources, etc. 

Being branded with a low IQ at a young age, in other words, is like being born poor. Due to family circumstances and the mechanisms of society, most people born poor will remain poor throughout their lives. But that doesn't mean anyone is *innately* poor or destined to be poor; there is always potential for any poor person to become rich. 

The happy reality is that IQ scores:
A) measure developed skills, not native intelligence.
B) can change dramatically.
C) don't say anything about a person's intellectual limits. 

More details below.  

Coming next in this blog: Should kids know their own IQs?


What is IQ?

IQ (short for "intelligence quotient") is a score derived from a collection of tests which rank academic achievement within a particular age group.

What do IQ tests measure?

IQ tests measure current academic abilities -- not any sort of fixed, innate intelligence. More specifically, the best-known IQ battery, "Stanford-Binet 5," measures Fluid Reasoning, Knowledge, Quantitative Reasoning, Visual-Spatial Processing, and Working Memory. Collectively, these skills are known as "symbolic logic." Among other things, IQ tests do not measure creativity;[i] they do not measure "practical intelligence" (otherwise known as "street smarts");[ii] and they do not measure what some psychologists call "emotional intelligence."

Harvard's Howard Gardner:

"The tasks featured in the IQ test are decidedly microscopic, are often unrelated to one another, and . . . are remote, in many cases, from everyday life. They rely heavily upon language and upon a person's skill in defining words, in knowing facts about the world, in finding connections (and differences) among verbal concepts . . . . Moreover, the intelligence test reveals little about an indivdual's potential for further growth."[iii]

Tufts' Robert Sternberg:

IQ problems tend to be "clearly defined, come with all the information needed to solve them, have only a single right answer, which can be reached by only a single method, [and are] disembodied from ordinary experience . . . . Practical problems, in contrast, tend to require problem recognition and formulation . . . require information seeking, have various acceptable solutions, be embedded in and require prior everyday experience, and require motivation and personal involvement."[iv]

How are IQ scores determined?

Raw individual test scores are converted so that they correlate perfectly to a bell curve representing the entire population of same-age students. The average score is always 100.

- An IQ score of 100 means that 50% of the people in your age group scored better, and 50% scored worse.

- An IQ score of 85 means that 84.13% of the people in your age group scored better, and 15.87% scored worse.

- An IQ score of 130 means that 2.28% of the people in your age group scored better, and 97.72% scored worse.

Can your IQ score change over time?

Absolutely. "IQ scores," explains Cornell University's Stephen Ceci, "can change quite dramatically as a result of changes in family environment (Clarke, 1976; Svendsen, 1982), work environment (Kohn and Schooler, 1978), historical environment (Flynn, 1987), styles of parenting (Baumrind, 1967; Dornbusch, 1987), and, most especially, shifts in level of schooling."[v]

If IQ scores can change over time, why do most people's IQ scores stay reasonable stable?

What any individual can achieve with the right combination of assets and gumption is entirely different from what most people actually do achieve. Most people settle into a particular academic standing early in life and do not substantially deviate from that standing. That's the inertia of life and human circumstance.

So IQ scores don't imply any sort of fixed or innate intelligence? 

Quite the contrary. We know that the abilities IQ measures are skills, and we know that people can earn these skills. "Intelligence," Robert Sternberg has declared, "represents a set of competencies in development." There is plenty of evidence, for example, that schooling raises overall academic intelligence.[vii] There is also evidence that most human beings are not reaching their cognitive or academic potential.[viii] Better schools and higher standards can raise the level of learning for nearly all students.

Don't genes limit our intelligence? Isn't intelligence "heritable?"

No, and no. Very sloppy science and journalism has led us to believe that what scientists call "heritability" (derived from twin studies) is the same thing as what we  ordinary folk call "heredity." In fact, they are not even remotely the same thing. Genes certainly do have an impact on intelligence, and everyone has their own theoretical limits, but every indication is that most of us don't come close to our true intellectual potential. More on this here.



[i] IQ scores do not identify the most successful and creative artists or scientists:

- Delis, D.C., Lansing, A., Houston, W.S., Wetter, S., Han, S.D., & Jacobsen, M., Holdnack, J., & Kramer, J. (2007). Creativity lost: The importance of testing higher-level executive functions in school-aged children. The Journal of Psychoeducational Assessment, 25, 29-40.

- Taylor, I. A., "A retrospective view of creativity investigation.' In Perspectives in creativity. A. Taylor and J. W. Getzels, eds., Aldine Publishing Co, pp. 1-36. 1975.


IQ does not distinguish the best chess players from others:

- Doll, J., and U. Mayr, 1987, "Intelligenz und Schachleistung - eine Untersuchung an Schachexperten."  [Intelligence and achievement in chess - a study of chess masters]. Psychologische Beiträge, 29: 270-289.


IQ scores have a weak correlation with nonacademic intelligence and with performance in everyday tasks in other cultures:

- Joan Miller, "A Cultural-Psychology Perspective On Intelligence," in Intelligence, heredity, and environment, Robert J. Sternberg, Elena Grigorenko Cambridge University Press, 1997. p. 292.


[iii]Howard Gardner, Frames of Mind, 1993, p. 18.


[iv] "Intelligence: Knowns and Unknowns," Report of a Task Force established by the Board of Scientific Affairs of the American Psychological Association, August 7, 1995.


Ceci, S. J. On Intelligence: A bio-ecological treatise on intellectual development. 2nd ed., Harvard University Press. 1996.

Ceci's citations:

Family environment
- Ann M. Clarke, Alan D. Clarke, Early Experience and the Life Path, Somerset, 1976.
- Dagmund Svendsen, Factors Related To Changes In IQ: A Follow-Up Study Of Former Slow Learners, Journal of Child Psychology and Psychiatry, Volume 24 Issue 3, Pages 405 - 413, 1982.
Work environment
- Melvin Kohn and Carmi Schooler, "The Reciprocal Effects of the Substantive Complexity of Work and Intellectual Flexibility: A Longitudinal Assessment" (with Carmi Schooler). 1978. American Journal of Sociology 84 (July): 24-52.
Historical environment
- Flynn, J. R. (1987). Massive IQ gains in 14 nations: What IQ tests really measure. Psychological Bulletin, 101,171-191. 
Styles of parenting
- D. Baumrind, "Child care practices anteceding three patterns of preschool behavior," Genetic Psychology Monographs, 75, 43-88, 1967.
- Sanford M. Dornbusch, Philip L. Ritter, P. Herbert Leiderman, Donald F. Roberts and Michael J. Fraleigh, " The Relation of Parenting Style to Adolescent School Performance," Child Development, Vol. 58, No. 5, Special Issue on Schools and Development (Oct., 1987), pp. 1244-1257. 
Individuals' IQ scores can change significantly over time:
- Harold E. Jones and Nancy Bayley, The Berkeley Growth Study, 1941 Society for Research in Child Development.


[vii]- Ceci, Stephen J., On Intelligence-- More or Less: A Bio-Ecological Treatise on Intellectual Development, Prentice Hall, 1990.

- Richard B. Darlington, "'The Bell Curve'--solid center or abnormal deviate?." Based on a talk given by Darlington at Cornell on April 24, 1995 


[viii]- Anders Ericsson, "Exceptional memorizers: made, not born," Trends Cogn Sci. 2003 Jun;7(6):233-235.

- Bartlett, J., and Byrd, R., "Team teaching verbal, mathematics, and learning skills, Howard University Center for Academic Reinforcement, 1980.

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