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The g Factor: The Science of Mental Ability
Jensen provides a comprehensive treatment of one of the major constructs of behavioral science―general mental ability―labeled the g factor by its discoverer, Charles Spearman. The g factor is about individual differences in mental abilities. In factor analyses of any and every large and diverse collection of measures of mental abilities, however varied the content of knowledge and skills they call upon, g emerges as the largest, most general source of differences between individuals and between certain subpopulations.
Jensen fully and clearly explains the psychometric, statistical, genetic, and physiological basis of g , as well as the major theoretical challenges to the concept. For decades a key construct in differential psychology, the g factor's significance for scholars and researchers in the brain sciences as well as education, sociology, anthropology, evolutionary psychology, economics, and public policy is clearly evident in this, the most comprehensive treatment of g ever published.
Jensen fully and clearly explains the psychometric, statistical, genetic, and physiological basis of g , as well as the major theoretical challenges to the concept. For decades a key construct in differential psychology, the g factor's significance for scholars and researchers in the brain sciences as well as education, sociology, anthropology, evolutionary psychology, economics, and public policy is clearly evident in this, the most comprehensive treatment of g ever published.
664 pages, Hardcover
First published February 28, 1998
About the author
Arthur R. Jensen
14 books26 followersArthur Robert Jensen was born August 24, 1923, in San Diego, California, the son of Linda Mary (née Schachtmayer) and Arthur Alfred Jensen, who operated and owned a lumber and building materials company. His paternal grandparents were Danish immigrants and his mother was of half Polish Jewish and half German descent. He studied at University of California, Berkeley (B.A. 1945), San Diego State College (M.A., 1952) and Columbia University (Ph.D., 1956), and did his doctoral thesis with Percival Symonds on the Thematic Apperception Test. From 1956 through 1958, he did his postdoctoral research at the University of London, Institute of Psychiatry with Hans Eysenck.
Upon returning to the United States he became a researcher and professor at the University of California, Berkeley, where he focused on individual differences in learning, especially the influences of culture, development, and genetics on intelligence and learning. He received tenure at Berkeley in 1962. He has concentrated much of his work on the learning difficulties of students in culturally disadvantaged environments. In 2003 he was awarded the Kistler Prize for original contributions to the understanding of the connection between the human genome and human society. In 2006 the International Society for Intelligence Research awarded Jensen its Lifetime Achievement Award. During Jensen's period in San Diego he spent time working as a social worker with the San Diego Department of Public Welfare.
Upon returning to the United States he became a researcher and professor at the University of California, Berkeley, where he focused on individual differences in learning, especially the influences of culture, development, and genetics on intelligence and learning. He received tenure at Berkeley in 1962. He has concentrated much of his work on the learning difficulties of students in culturally disadvantaged environments. In 2003 he was awarded the Kistler Prize for original contributions to the understanding of the connection between the human genome and human society. In 2006 the International Society for Intelligence Research awarded Jensen its Lifetime Achievement Award. During Jensen's period in San Diego he spent time working as a social worker with the San Diego Department of Public Welfare.
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Displaying 1 - 9 of 9 reviews
February 10, 2011
Until very recently, I had not realized the enormous progress made in the field of differential psychology over the past 100 years, which makes for very different and more engaging intellectual study than the stale Freudianism that the humanities have been chewing on for the past 40 years.
The g factor I found to be a thoughtful and thorough book, and I quite enjoyed Jensen's relaxed but serious voice. His discussion of the Flynn effect, for instance, was for me enormously comprehensive, and left no stone unturned. That said, a fair amount was over my head (my mathematics are particularly deficient).
The g factor itself is an amazingly vexing and mysterious "nexus," in the best tradition of scientific puzzles.
The g factor I found to be a thoughtful and thorough book, and I quite enjoyed Jensen's relaxed but serious voice. His discussion of the Flynn effect, for instance, was for me enormously comprehensive, and left no stone unturned. That said, a fair amount was over my head (my mathematics are particularly deficient).
The g factor itself is an amazingly vexing and mysterious "nexus," in the best tradition of scientific puzzles.
September 15, 2020
I found the "The g Factor:..." to be an enlightening and thoroughly researched book on a fascinating topic. Although the basic premise, that intelligence matters and that it is primarily inherited was evident, the book was rarely boring. The basic premise regarding intelligence was broadened by Jensen to explain intelligence in statistical and physical terms with forays into g's manifestations in life. The book will not appeal to people without a strong interest in statistics; it will not appeal to people who believe that the environment is the primary shaper of our personalities. I have two criticisms of the book. The book could have been composed better; sentences were sometimes very long with an excessive flourish. My second criticism concerns the author's purpose. Although I have no doubt as to the validity of the information presented, I wondered about the emphasis on black and white racial differences. I would have liked to see more balance in the examination of racial differences. Overall, I found the book to be fascinating and enlightening.
October 26, 2015
The g Factor is a comprehensive analysis conducted by Jensen look at the general intelligence across a wide range of factors and their implications. He looked at gender difference (which found relatively little differences), heritability (some evidence suggesting this), job performance (highly predictive), etc.
It may be complex for a non-psychological reader but worth a read to understand more about differential psychology.
It may be complex for a non-psychological reader but worth a read to understand more about differential psychology.
July 3, 2020
The definitive, data-driven, scholarly exposition on the field of differential psychology, imperative for all who wish to have journeyman sharpness and clarity in our understanding of intelligence - it's nature, controversies, limitations, and future.
December 27, 2020
The most definitive account of psychometric I have ever read.
August 13, 2024
JENSEN'S NEXT-TO-LAST BOOK DEFENDING HIS VIEWS ON IQ, ETC.
Jensen says in the "Acknowledgements" section, "Especially deserving of credit for supporting much of the empirical research I have done on the g factor ... at a time when few foundations or granting agencies would consider supporting research aimed at exploring the nature and implications of g in areas considered politically sensitive, are the Pioneer Fund and its admirably intrepid president, Harry F. Weyher, whose mission has been to lend support to pioneering efforts in scientific research areas that in academe are often considered unpopular or even taboo..." (Pg. xiii)
He admits, "No other term in psychology has proved harder to define than `intelligence.' Not that psychologists haven't tried... even the experts in this field still cannot agree on a definition. In fact, there are nearly as many different definitions of `intelligence' as there are experts." (Pg. 46)
He acknowledges that "there is almost no limit to the possible idiosyncratic reasons for failing a given item [on a test]. It is probable, however, that some part of the reason for failing a particular item is the person's standing on the general ability measured by the test as a whole..." (Pg. 313)
He addresses the counter-argument of Thomas Sowell (reprinted in Race and Culture), saying, "Thomas Sowell] does not offer a formal or explanatory theory, but rather a broad analogy between American blacks and other ethnic and national groups that have settled in the United States at different times in the past. Sowell points out that many immigrant groups performed poorly on tests at one time (usually soon after their arrival in America) and had relatively low educational standing, which limited their employment to low-paying jobs. The somewhat lower test scores of recent immigrants are usually attributable to unfamiliarity with the English language, as evidenced by their relatively superior performance on nonverbal tests...
"Sowell views the American black population as a part of this same general phenomenon and expects that in due course it, too, will rise to the overall national level... But Sowell's analogy between blacks and other immigrant groups seems strained when one examines the performance of comparatively recent arrivals from Asia.... despite their different language and culture, they have scored as high as the native white population on nonverbal IQ tests and they often exceed the white average in scholastic performance." (Pg. 512)
While most of us do not find Jensen's work at all persuasive, one can still read his arguments and decide for oneself.
Jensen says in the "Acknowledgements" section, "Especially deserving of credit for supporting much of the empirical research I have done on the g factor ... at a time when few foundations or granting agencies would consider supporting research aimed at exploring the nature and implications of g in areas considered politically sensitive, are the Pioneer Fund and its admirably intrepid president, Harry F. Weyher, whose mission has been to lend support to pioneering efforts in scientific research areas that in academe are often considered unpopular or even taboo..." (Pg. xiii)
He admits, "No other term in psychology has proved harder to define than `intelligence.' Not that psychologists haven't tried... even the experts in this field still cannot agree on a definition. In fact, there are nearly as many different definitions of `intelligence' as there are experts." (Pg. 46)
He acknowledges that "there is almost no limit to the possible idiosyncratic reasons for failing a given item [on a test]. It is probable, however, that some part of the reason for failing a particular item is the person's standing on the general ability measured by the test as a whole..." (Pg. 313)
He addresses the counter-argument of Thomas Sowell (reprinted in Race and Culture), saying, "Thomas Sowell] does not offer a formal or explanatory theory, but rather a broad analogy between American blacks and other ethnic and national groups that have settled in the United States at different times in the past. Sowell points out that many immigrant groups performed poorly on tests at one time (usually soon after their arrival in America) and had relatively low educational standing, which limited their employment to low-paying jobs. The somewhat lower test scores of recent immigrants are usually attributable to unfamiliarity with the English language, as evidenced by their relatively superior performance on nonverbal tests...
"Sowell views the American black population as a part of this same general phenomenon and expects that in due course it, too, will rise to the overall national level... But Sowell's analogy between blacks and other immigrant groups seems strained when one examines the performance of comparatively recent arrivals from Asia.... despite their different language and culture, they have scored as high as the native white population on nonverbal IQ tests and they often exceed the white average in scholastic performance." (Pg. 512)
While most of us do not find Jensen's work at all persuasive, one can still read his arguments and decide for oneself.
March 18, 2026
What a scholar! Profound thesis, fascinating trivia.
Jensen's definitions and descriptions of his science are fascinating. g stands for General Ability. It is neither IQ nor intelligence itself. Intelligence, per Jensen, is the capacity of all animals to perceive and act upon the natural world.
The Intelligence Quotient is a statistical artifice that maps individuals' problem solving abilities into a linear scale according to a Gaussian bell-curve distribution. By definition the average IQ is 100 and the standard deviation (SD) 15. By the properties of the bell curve approximately 2/3 of the population falls within one SD of the median, that is, between 85 and 115.
However, as Jensen points out repeatedly, general ability is not a linear function. The discriminators are whether or not an individual can solve specific problems. There is no way to define a lineal relationship between two individuals if once can figure out (for instance) the lowest primo number greater than 90 and another cannot, or one can figure that context requires the word above to be "prime" not "primo" and another cannot. There is no metric for "g" itself. Rather, all tests of mental ability have a degree of "g loading." Psychometrics is the science of assessing and manipulating information about a quality that cannot be measured directly.
Jensen devotes much energy to defending the validity of "g", this thing that defies direct measurement. It is real because:
a) It is statistically "there." It is highly correlated among myriad tests.
b) It works in the real world. There is no single discriminator that approaches the value of "g", usually proxied by an IQ test score, as a predictor of educational or job performance.
c) It has equal predictive power for both sexes, all ages and all populations of mankind. It is independent (as he takes endless pages to prove) of race, language and socio-economic status (SES).
d) Many seemingly unrelated kinds of tests all turn out to measure the same thing. Tests may be verbal or pictorial, or may simply measure the time it takes to react to and act upon a visual or auditory stimulus.
e) By adulthood it no longer has much to do with advantages such as hearing Mozart in the womb or a Montessori kindergarten, or disadvantages such as Jim Crow and slavery.
The other reviews of this book are quite good. Some of Jensen's many fascinating observations:
o Incest is a bad idea. The offspring have a significant intelligence deficit.
o Smart parents, alas, can't count on having equally smart kids. On average their intelligence regresses halfway back to the mean (100 for white Americans). On the bright side, the average people manage by dumb luck to produce enough smarties for each succeeding generation.
o Breast feeding makes a huge difference, about 7 IQ points. Blacks do not breast feed as often or as long as whites. Big, easy change to make in society.
o The factors generally agreed to comprise "g" differ among races and sexes. Blacks exceed whites in short term memory. Men exceed women in spatial intelligence. When the many individual factors are aggregated they reveal different means for different races, with whites in the middle with an average of 100.
o Individuals with IQs below 70 are generally considered to be retarded. White retarded kids frequently look and act somehow different, while retarded kids of other races are more normal in terms of socialization, motor skills and energy. This is related to the two types of retardation, familial and organic. In simple words, there is something "wrong with" an organically retarded child. A bad forceps delivery, spina difida or one of a number of identifiable anomalies. Familial retardation, on the other hand, simply represents a bad spin of the chromosomal wheel of fortune that is sexual reproduction. The odds are higher in populations whose median IQs are lower.
o Cause for concern: If Vanhansen and Lynn are right in "IQ and the Wealth of Nations" there are perhaps a dozen countries in which the average citizen would be considered retarded and hence marginally educable by U.S. standards.
o Illiteracy is not always a matter of reading. Below the threshold of retardation people often have the same inability to understand a sentence whether it is written or spoken. The issue is having enough "g" to make sense out of the words.
o People with lower IQs are markedly more fertile than those with higher IQs. This dysgenic (opposite of eugenic) trend stands to lower "g" within the U.S. population. Average intelligence will of course remain at 100 because by definition it is the population mean.
Jensen comes across through this book as first and foremost an inquisitive mind, a scientist. He often states with unashamed candor that he (nor anybody else) knows the answer to some knotty problems of psychometrics, like the Flynn effect that shows overall intelligence rising 3 points per generation. Contrast his thoroughness and openness with the tone of advocacy found in Stephen Jay Gould (Mismeasure of Man) and sites such as fairtest dot org. Steven Pinker describes in "The Blank Slate, the Modern Denial of Human Nature" the extreme and prolonged abuse Jensen has taken from the academic community. I'm happy to report he hasn't lost his sense of balance. Or sense of humor.
Jensen's definitions and descriptions of his science are fascinating. g stands for General Ability. It is neither IQ nor intelligence itself. Intelligence, per Jensen, is the capacity of all animals to perceive and act upon the natural world.
The Intelligence Quotient is a statistical artifice that maps individuals' problem solving abilities into a linear scale according to a Gaussian bell-curve distribution. By definition the average IQ is 100 and the standard deviation (SD) 15. By the properties of the bell curve approximately 2/3 of the population falls within one SD of the median, that is, between 85 and 115.
However, as Jensen points out repeatedly, general ability is not a linear function. The discriminators are whether or not an individual can solve specific problems. There is no way to define a lineal relationship between two individuals if once can figure out (for instance) the lowest primo number greater than 90 and another cannot, or one can figure that context requires the word above to be "prime" not "primo" and another cannot. There is no metric for "g" itself. Rather, all tests of mental ability have a degree of "g loading." Psychometrics is the science of assessing and manipulating information about a quality that cannot be measured directly.
Jensen devotes much energy to defending the validity of "g", this thing that defies direct measurement. It is real because:
a) It is statistically "there." It is highly correlated among myriad tests.
b) It works in the real world. There is no single discriminator that approaches the value of "g", usually proxied by an IQ test score, as a predictor of educational or job performance.
c) It has equal predictive power for both sexes, all ages and all populations of mankind. It is independent (as he takes endless pages to prove) of race, language and socio-economic status (SES).
d) Many seemingly unrelated kinds of tests all turn out to measure the same thing. Tests may be verbal or pictorial, or may simply measure the time it takes to react to and act upon a visual or auditory stimulus.
e) By adulthood it no longer has much to do with advantages such as hearing Mozart in the womb or a Montessori kindergarten, or disadvantages such as Jim Crow and slavery.
The other reviews of this book are quite good. Some of Jensen's many fascinating observations:
o Incest is a bad idea. The offspring have a significant intelligence deficit.
o Smart parents, alas, can't count on having equally smart kids. On average their intelligence regresses halfway back to the mean (100 for white Americans). On the bright side, the average people manage by dumb luck to produce enough smarties for each succeeding generation.
o Breast feeding makes a huge difference, about 7 IQ points. Blacks do not breast feed as often or as long as whites. Big, easy change to make in society.
o The factors generally agreed to comprise "g" differ among races and sexes. Blacks exceed whites in short term memory. Men exceed women in spatial intelligence. When the many individual factors are aggregated they reveal different means for different races, with whites in the middle with an average of 100.
o Individuals with IQs below 70 are generally considered to be retarded. White retarded kids frequently look and act somehow different, while retarded kids of other races are more normal in terms of socialization, motor skills and energy. This is related to the two types of retardation, familial and organic. In simple words, there is something "wrong with" an organically retarded child. A bad forceps delivery, spina difida or one of a number of identifiable anomalies. Familial retardation, on the other hand, simply represents a bad spin of the chromosomal wheel of fortune that is sexual reproduction. The odds are higher in populations whose median IQs are lower.
o Cause for concern: If Vanhansen and Lynn are right in "IQ and the Wealth of Nations" there are perhaps a dozen countries in which the average citizen would be considered retarded and hence marginally educable by U.S. standards.
o Illiteracy is not always a matter of reading. Below the threshold of retardation people often have the same inability to understand a sentence whether it is written or spoken. The issue is having enough "g" to make sense out of the words.
o People with lower IQs are markedly more fertile than those with higher IQs. This dysgenic (opposite of eugenic) trend stands to lower "g" within the U.S. population. Average intelligence will of course remain at 100 because by definition it is the population mean.
Jensen comes across through this book as first and foremost an inquisitive mind, a scientist. He often states with unashamed candor that he (nor anybody else) knows the answer to some knotty problems of psychometrics, like the Flynn effect that shows overall intelligence rising 3 points per generation. Contrast his thoroughness and openness with the tone of advocacy found in Stephen Jay Gould (Mismeasure of Man) and sites such as fairtest dot org. Steven Pinker describes in "The Blank Slate, the Modern Denial of Human Nature" the extreme and prolonged abuse Jensen has taken from the academic community. I'm happy to report he hasn't lost his sense of balance. Or sense of humor.
Read
March 22, 2013The book is controversial.. keeps you asking questions but all in all a non-put-downer
Want to Read
October 5, 2013skipped as too much detail, possible traverse to explore policy implications
This entire review has been hidden because of spoilers.
Displaying 1 - 9 of 9 reviews