The Terman Study






Importance: It Showed That Gifted Children Are Taller, Better-Looking, and More Successful Than Average
     The Terman-Study results are quoted in nearly every discussion about what becomes of gifted children.
      Prior to the middle of the 19th century, youthful prodigies were regarded "with a mixture of admiration, awe, and hopeful expectation. His parents were envied, and the child was likely to be made the protęgé of a prince or king."
* 

* - (Genetic Studies of Genius, Vol. IV, "The Gifted Child Grows Up", Terman and Odum, Stanford University Press, 1949, pg. 1)

     Beginning about 1850, it became fashionable to perceive highly intelligent children as misfits who "burned out", or overtaxed their brains and died young. They were thought to be pale, asthenic,  bespectacled, and stoop-shouldered, and headed for adult stupidity or insanity. "The myth became prevalent that many of the great geniuses were dunces in childhood." The view developed that a rich and well-balanced maturity depends upon the prolongation of infancy and the fullest experience with each developmental stage. The bright child should protected from intellectual stimulation, "and any tendency toward early cleverness should be positively discouraged."
    This must have been very comforting to the average citizen, and to the intellectually challenged. That smart kid in class would pay for it when she/he grew up.
    The Terman Study showed that gifted children grow up to become gifted adults, and that they tend to be  successful, well-adjusted, and long-lived.... healthier, wealthier, and wiser. They're taller and better-looking, on average, and they're an invitation to uncomfortable comparisons for the rest of us. It's hard not to feel competitive with them, and at a competitive disadvantage.
    Interestingly, the Terman screening of the population revealed the fact that, on the wings of the bell curve, out-lying ratio-IQs aren't distributed in accordance with a Gaussian distribution. (Some of us are exploring the hypothesis that the natural logarithms of IQs are Gaussian distributed*.)


* - To obtain the logarithm of the ratio-IQ, divide the IQ by 100 to convert it to a decimal fraction. Then take its natural logarithm on any scientific calculator. Multiply the resulting fraction by 100 to convert it back into an IQ, and add 100 to it. The resulting number is the deviation "IQ", with a standard deviation of approximately 15 points. Note the interesting fact that there is nothing in this calculation that sets the standard deviation to be 15.


Background: (Did They Make A Mistake By Letting Teachers Pre-Select the Candidates?) In 1921, Dr. Lewis M. Terman and Dr. Catherine Miles Cox were awarded a grant of $34,300 (equivalent to, perhaps, $340,000 today) by the Commonwealth Foundation to conduct a lifelong study of 1,444 gifted schoolchildren selected from a population estimated to be at least 268,000 California schoolchildren. To this was added another $8,000 in cash and $6,000 in services, plus additional unbudgeted services, bringing the total to more than $50,000 (~$500,000 in today's dollars). This study is still underway among the "Termites" who are still alive. These children were pre-selected by their teachers as having shown signs of giftedness, and were then further filtered by intelligence testing. Dr. Terman says (Genetic Studies of Genius - Vol. I - Mental and physical Traits of a Thousand Gifted Children, Terman, et al, Oxford University Press, London, 1925, pg. 20),
    "The faults of subjective ratings have been sufficiently exposed in numerous investigations to show their great unreliability when used alone. Such ratings are usually based too largely on the child's class work and are almost certain to weigh too lightly the age factor. Age-grade status is perhaps a better criterion, but its value is limited (1) by the variable standards in different cities, or even in different schools of the same city, and (2) by the difficulty of equating various degrees of acceleration for children of the different ages. The first-named objection is the most serious, More0ver the age-grade status of a given child rests ultimately upon a teacher's rating; that is, upon a judgment of fitness for promotion. It is also likely to be affected by age of entering school, regularity of attendance, adaptability to school requirements, and various other factors having nothing to do with intelligence. Achievement tests, although they are an objective method, were not seriously considered as they would have been more costly than intelligence tests and inferior to them as measures of native ability."

    (Knowing what we know today about the low correlation between teachers' assessments of giftedness--particularly, extreme giftedness--and children's actual levels of giftedness, it would seem as though there would have been room for judgment errors in the 1921 screening. On the other hand, undoubtedly Dr. Terman did the best he could with the resources he had, and produced a landmark study.)
Criteria for Enrollment in the Study
    The initial sifting method consisted of a combination of teachers' ratings and the age-grade status of the children. (In those days, apparently, the gifted were commonly encouraged to skip grades, with whatever combination of beneficial and harmful consequences that may have had.) Then the nominees, ranging from 2% of the students in Los Angeles' poorer schools, to 20% of the student population in communities like, I suppose, Berkeley and Hollywood, and averaging 6% to 8%, were given the National Intelligence Test as a screening tool. Those who passed muster were then given an abbreviated version of the 1916 Stanford-Binet IQ test. For children below 11, the entrance criterion was an IQ of 140. For children above 11, ceiling effects reduced the scores of the brighter students. Consequently, the eligibility thresholds were reduced accordingly, from 139 at 11 to 11½ to 136 at 13 and to 132 at 14. Beyond 14, the Terman Group Test (T. G. T.) was used for high school students. Unfortunately, there don't seem to be any conversion tables in Dr. Terman's book relating IQ's to T. G. T. scores. A raw score of 195 is the entry level score for children 15 and older, and presumably corresponds to an IQ of 140 and to a mental age of 21. However, the two highest scores made on this test are in the 215-219 interval, so it's difficult to assign an IQ to them.

Nominally, the study was to include the top 1% of the scorers on the S-B test (IQ = 136 and above), but the 1,528 schoolchildren that they enrolled in the study represent only about 0.6% of 250,000. Furthermore, because there are more IQs of 136+ than would be expected on the basis of a Gaussian normal distribution, a 1921 S-B IQ of 136 would correspond to the top 2% of the population. In reality, in the light of the numbers of children they enrolled in each 10-point IQ range, I suspect that they took some children in the IQ 136-150 range, and missed a lot of others.
    About 46 children in the group were included because they demonstrated special talents.

Criticisms: (1) Too Many Children of Professionals; (2) Intervention by Dr. Terman; (3) Labeling Anyone with an an IQ of 140+ a Genius  One of the criticisms that has been leveled at the study is that 30% of the children came from professional-technical families rather than the 3% that characterized the average population. Also, there was an under-representation of minorities in the study cohort. Another criticism was that in their adult years, Dr. Terman sometimes intervened on behalf of his "Termites", helping them in various ways.
    Another obvious criticism, although I don't remember hearing much about it at the time, was the fact that anyone with an IQ of 140+, occurring about to about one in every 80 people, was designated a genius. More than 1,000,000 U. S. citizens satisfied this definition of genius in 1921. That's a lot of promise to fulfill, and they didn't.
    (It's easy to criticize with 20/20 hindsight, but at the time this study began, the 1916 Stanford-Binet IQ test was only five years old, and IQ testing was in its infancy in the United States.)

Many More Children with Very-High IQs Than a Bell Curve Would Predict:  The Terman Study unearthed far more high-IQ scores in its 1921-22 screening than would be predicted by a Gaussian distribution(cf "Genius", by Hans Eysenck, pg. 58). As Dr. Eysenck puts it,
    "Leta Hollingworth (1942) in her work with children with IQs over 180 found far more than compatible with a normal distribution, and so did Terman (1925) in his search for children above 140 IQ."
    The highest IQ score found during the screening was 200, a score that would be expected to occur only once among every 5,000,000,000 test-takers, and 29.6 points above the highest expected 1-in-250,000 score of 171.4. The chance of finding such a score among 268,000 schoolchildren would thus have been 1 in 20,000, or to say it another way, it suggests that there are 20,000 times as many people with an IQ of 200 as would have been expected on the basis of a Gaussian distribution. There were 26 children who achieved scores of 180 or above (cf Ellen Winner's "Gifted Children: Myths and Realities"). There should be only one such score in every 3,500,000 individuals. Consequently, the frequency with which IQ's of 180+ occurred in the 1921-22 screening was about 365 times the number that would have been predicted by a Gaussian distribution. Seventy-seven children were identified with IQ's that fell above 170 (cf "Genius", pg. 60), whereas only 1.5 would have been predicted, an "enrichment ratio" of about 49 to 1. There were about 12 times as many Termites with IQ's of 160 as would have been expected, and about 3.4 times as many with IQ's of 150 as there should have been.
    Dr. Terman pointed out the deviation from a Gaussian distribution in a paper he published in 1925. 

These Deviations from a Bell Curve Seem to Have Been a Closely Guarded Secret in the 1940's and the 1950's
    What is shocking to me about this is that when I began reading about IQ testing in the mid-40's, there was no mention of the fact that IQ distributions deviated blatantly from a Gaussian normal distribution. The only hint of it that I remember was Leta Hollingworth's mentioning the fact that she was finding 2 or 3 children per million in New York City with IQ's above 180 rather than the one per million that would be expected. (Actually, a Gaussian distribution calls for 1 IQ of 180 or above only in every 3.5 million people. The actual frequency of occurrence turns out to be, perhaps, 45 per million.) Nor did I hear anything about it as an undergraduate psychology major at Ohio State in the early 50's..
    Table 1, below, shows the way the Terman numbers may be mapped into equivalent deviation IQ's.

Table 1 - IQ Frequencies Observed in the Terman Study in 1921

Ratio
IQ

Expected
Frequency of 
Occurrence

Observed
Frequency of
Occurrence

Equivalent
Deviation IQ

Ratio of Observed to Expected

201

1 : 7,000,000,000

1 : 268,000

171.6

26,000

190+

1 : 110,000,000

Unavailable

 Unavailable

Unavailable

 180+

1 : 3,500,000

1 : 10,300

159.6

340

170+

1 : 160,000

1 : 3,500

 155

49

160+

1 : 11,000

1 : 900

 149

12

150+

1 : 1,100

1 : 340

144

3.4

140+

1:160

1 : 100

137

1.6

Terman Hyperabundance of the Hyperbright Found in Other Studies As Well (Leading to a Switch to "Deviation IQs"?)
    These results agree well with other, later studies of larger populations. A landmark University of London Master's thesis by Geoffrey Thomas Sare in 1951 generated the following table (Table 2):

Table 2 - IQ Frequencies Observed by Geoffrey Thomas Sare in 1951

Ratio
IQ 

Expected
Frequency of 
Occurrence

Observed
Frequency of
Occurrence

Equivalent
Deviation IQ 

Ratio of
Observed to
Expected

196

1 : 1,000,000,000

1 : 300,000

172

3,333

190

1 : 93,300,000

1 : 109,000

 169

910

 180

1 : 3,490,000

1 : 24,000

 163

146

170

1 : 167,000

1 : 5,040

 157

32

160

1 : 11,500

1 : 1,170

 150

10

150

1 : 1,140

1 : 286

143

4

140

1 : 161

1 : 80

136

2

    The Termites' deviation-IQs actually reflect slightly higher-than-expected IQs, consistent with an enriched population. However, the Termites' score distribution closely mirrors what the Sare study would predict.
A Log-Normal Distribution Fits the Terman and Geoffrey Sare Data Very Well.
    Although the scores themselves deviate from the tails of a bell curve, the natural logarithm of the Gaussian error function is normally distributed. John Scoville has observed that a log-normal distribution fits Vernon Sare's data very well, as shown in Table 3 below. The log-normal distribution equates the deviation IQ to the logarithm of the ratio-IQ.

   Deviation-IQ = ln(ratio IQ/100) = 106.667 ln(ratio IQ/100) + 100,

And conversely,

    Ratio-IQ = 100 exp((deviation-IQ - 100)/106.667)

Table 3 - IQ Frequencies Predicted by a Log-Normal Model

Ratio
IQ 

Ratio-IQ
Frequency of 
Occurrence

Deviation-IQ
Frequency of
Occurrence

Equivalent
Deviation IQ 

Ratio of
Expected to
Observed

196

1 : 1,000,000,000

1 : 284,000

171.8

3,500

190

1 : 93,000,000

1 : 105,000

 168.5

886

 180

1 : 3,500,000

1 : 29,000

 162.7

121

170

1 : 167,000

1 : 4,600

 156.6

36

160

1 : 11,500

1 : 1,170

 150

10

150

1 : 1,140

1 : 295

143.25

4

140

1 : 161

1 : 80

135.8

2

   It has been discovered that although Gaussian distributions fit observed IQ distributions well within one or two standard deviations of the mean value of 100 (between IQ levels of 68 and 132), they rapidly become inaccurate for IQ's lying outside this range. Hans Eysenck discusses this on page 58 in his book "Genius", observing that Cyril Burt proposed a Pearson Type IV distribution to fit the observed data. A Pearson Type IV curve predicts that an IQ of 200 will occur with a frequency of 6.2 per million, and one IQ of 160 per 1,100 test subjects. The 6.2 per million agrees well with the Terman data, but not as well with the Vernon Sare results (which predict 2 per million). On the other hand, one IQ of 160 per 1,100 test subjects agrees well with the Sare table above.
Caveat:
    I also need to flag the fact that Darryl Miyaguchi is not sure about the reality of the Geoffrey Thomas Sare paper that several of us have quoted. Darryl is going to try to make sure that such a Master's thesis exists. In the meantime, I need to raise a flag concerning this "data" pending Darryl's investigation, since Im relying upon it for confirmation of the log-normal model that John Scoville and Dr. Robert Dick have devised.
    Of course, the Terman data fits the log-normal model well, as shown by comparing Table I with Table III.

Distributions of Other Physical Parameters, Such as Height, Are Also Non Gaussian It's worth noting that Gaussian distributions for other physical parameters such as height also predict frequencies of occurrence fairly accurately for values close to the norm, but become increasingly erroneous on the wings of the curve. For example, if the average male height is taken to be 5' 8', with a standard deviation of 4 inches, heights greater than 7' 8" and less than 3' 8" should occur in fewer than one in a billion cases. In practice, their frequencies of occurrence are much higher than that.

Conclusions: "Termites" Were Taller, Better-Educated, More Successful Than Average
    The most significant result of the Terman Study was the revelation that the Termites were, on the whole, taller, better educated, more successful, and better adjusted than average. For example, 70% graduated from college, with 67% of the men and 60% of the women continuing on to graduate school (in the 30's)..Among the men, 86% were to be found in the professions, the semi-professions, and higher business. No gifted men were found on the lowest occupational level, compared to 13% of the general population.
But—No Geniuses Were Found
    At the same time, it was also the case that no geniuses emerged from the group. The two members of the screened population who became Nobel Laureates--Drs. William Shockley, for the invention of the transistor, and Dr. Luis Alvarez, for the liquid hydrogen bubble chamber--failed to make the cut admitting them to the program. However, a couple of points might need to be considered. In Dr. Shockley's case, three men shared the Nobel Prize: Dr. Shockley, Dr. John Bardeen, and Dr. Walter Brittain. Dr. Bardeen was a theoretician who was the first physicist to receive a second Nobel Prize in physics (for superconductivity). (As a child, could Dr. Alvarez have spoken English as a second language, and have faced special problems on an English-based IQ test.?) Also, the students had to first be selected by their teachers, and later-studies revealed that teachers have an imperfect track record in identifying the gifted.
    But the fact remains that the there were two Nobel-Prize winners in physics who were among those screened by the Terman Study and they were rejected as having IQs too low to be included in the program.

But—How Many Geniuses Among 268,000 People Anyway?
   In assessing the accomplishments of the Termites, it's important to realize that 250,000 people corresponds to the population of a city the size of Grand Rapids, Michigan, or Ft. Lauderdale, Florida. Another way to say it is that 250,000 represent 0.1% of the current U. S. population. How many geniuses will Grand Rapids produce? Ft. Lauderdale? How many would 0.1.% of the geniuses in the United States comprise. The Terman Study produced 70 individuals who, by or before the age of 40, had qualified for American Men of Science (before World War II). Three had been elected to the national Academy of Sciences. ten more appeared in Directory of American Scholars, and 31 made it into Who's Who in America. Thirteen of these were faculty members, eight were top-ranking executives, and three were diplomats. Of the rest, one was an internationally known scientist who was the provost of a leading university, another was a distinguished literary scholar who was the vice-chancellor at one of the country's largest universities. A third, with a doctorate in theology, was the president of a small denominational college. It also included a famous oceanographer who headed a major institute of oceanography, the dean of a leading medical school, and an internationally known physiologist who directed an internationally known laboratory. Collectively, they had published 2000+ scientific and technical papers, 60 books and monographs, 230 patents, 33 novels, 375 short stories, and 265 articles. And all of these accomplishments had been registered by or before the age of 40.
Age At Which the Termites Learned to Read
    "Terman found back in the 1920's that the age at which reading began was one of the few traits that distinguished the more gifted from the not-as-gifted."
    In the 1921 study, among children a or above IQ 170, only 43% began to read before they were 5, and only 13% of these learned to read before the age of 4. The median reading age was a little above 5. 57% learned to read when they were 5 or older..
    By contrast, In Leta Hollingsworth's study of "Children Above 180 IQ", 83% were reading before age 5, 67% were reading before the age of 4, 58% were reading before 3,, and 8% were reading before the age of 2. Their average reading age was 3.67.
    A similar study by Van Tassel and Baska found that 80% were reading before 5, and 55% were reading before 4.
    In Mirica Gross' 1980's study of extremely gifted children in Australia, among the four children who scored at the 200 level on the 1973 edition of the Stanford Binet, Adrian was reading before 2, Christopher was reading between 2 and 3, Ian was reading before 2, and Hadley was reading at 18 months. Christopher and Ian scored exactly 200, while Adrian, at 6, scored 233.

Did the Terman Study Miss More Potentially-Eligible Children Than It Enrolled?
    You'll remember that I mentioned at the outset that the Terman Study only enrolled about 0.6% of the 250,000 schoolchildren that it screened. At the same time, the test claimed to have screened the top 1%. But that would have corresponded to a ratio IQ of 137 or a deviation IQ of 133.5 or about the top 2% of all the schoolchildren. So what happened to the other 1.3%? As you'll see below, there is reason to believe that the study missed more children who would later become eligible adults than it picked up.
Follow-Up: The Termites Adult IQs
    In 1940, when the average age of the Termites was 29, they were given a follow-up IQ test called the Concept Mastery Test (CMT). Table 4, below, shows the number of people who took the CMT in each IQ range, together with their average IQ scores on the CMT. What we're seeking here is a comparison between the "Termites" childhood IQ scores and their adult IQ scores.

Column 1 lists the childhood ratio-IQ ranges.
Column 2 lists the estimated deviation IQ ranges equivalent to Column 1's ratio IQ ranges.
Column 3 lists the estimated average ratio-IQ within each range in Column 1.
Column 4 lists the estimated average deviation-IQ within each range in Column 2.
Column 5 lists the number of people who took the adult (CMT) IQ test in 1940 whose childhood IQs had fallen within the ranges in Column 1.
Column 6 lists the average adult CTM scores for each childhood IQ range.
Column 7 lists the average declines in IQ, from child to adult, if the CMT measured ratio IQs.
Column 8 lists the average declines in IQ, from child to adult, if the CMT measured deviation IQs.

Table 4 – The Termites Average Childhood and Adult IQs

Childhood Ratio IQ Ranges

Childhood Deviation IQ Ranges

Childhood Average* Ratio IQ

Childhood Average* Deviation IQ

N

CMT-T Average Adult Score

IQ Declines, if CMT Measured Ratio IQs

IQ Declines, if CMT Measured Deviation IQs

170

155

178

159

48

155.8

-22

-4.2

160-169

150-156

163

152

70

146.2

-17

-5.8

150-159

143-149

153

145

200

136.5

-16.5

-8.5

140-149

136-143

143

138

344

131.8

-11

-6.2

135-139

132-135

136

133

41

114.2

-22

-18.5

* - Guesstimate

    At first blush, since deviation iQs weren't introduced until the early 1960's, one would suppose that the CMT could only be measuring ratio IQs. However, Terman, et al, must have been well aware of the over-representation of high scores among his "Termites". It's possible that they normed the CMT on the basis of percentiles, and assigned IQ scores based upon percentile rankings, thereby, in effect, generating deviation IQ scores.
The data in Columns 1, 5, and 6 are derived from a wonderful discussion of the severely gifted written by Grady Towers, entitled, "The Outsiders". In it, Grady says,

    "To obtain such insight requires close observation by a gifted observer. Fortunately, those insights are available to us in Leta S. Hollingworth's book, Children above 180 IQ. Hollingworth not only observed her subjects as children, she also continued to maintain some contact with them after they had reached maturity. So although her book is ostensibly about children, it is in fact laced throughout by her observations on exceptionally gifted adults as well.
    "Before examining Hollingworth's findings, however, it is necessary to explain how childhood IQs are related to adult mental ability. As a child ages, his IQ tends to regress to the mean of the population of which he is a member. This is partly due to the imperfect reliability of the test, and partly due to the uneven rate of maturation. The earlier the IQ is obtained, and the higher the score, the more the IQ can be expected to regress by the time the child becomes an adult. So although Hollingworth's children were all selected to have IQs above 180, their adult status was not nearly so high. In fact, as adults, there's good reason to believe that their abilities averaged only slightly above that of the average Triple Nine member. Evidence for this conjecture comes from the Terman research data. Terman observed the following relationship between childhood IQs on the Stanford-Binet and adult status on the Concept Mastery test form T.

    "The average childhood IQ score for those with childhood IQs above 170 was 177.7 for men, and 177.6 for women. That's quite close to the 180 cutoff used by Leta Hollingworth in selecting her subjects. Note that Terman's subjects who scored above 170 IQ as children averaged 155.8 on the CMT-T at age 41, a score quite close to the 155.16 made by the average Triple Nine member. Such a close match makes it reasonable to generalize Hollingworth's findings to members of both the Triple Nine Society and the Prometheus Society.

A Rift Within the Lute: Grady Towers vs. Hans Eysenck
    There's some confusion written into this last paragraph. Grady compares the childhood ratio-IQ average of 177.7 for the children who scored 170 or above as children with their adult average CMT IQ of 155.8, treating the CMT score as a ratio-IQ. He then compares this 155.8 IQ score with the 155.16 average IQ of Triple Nine Members. But the entry-level IQ required for admission into the Triple Nine Society is a deviation IQ of 150, corresponding to a ratio IQ of 160. Obviously, the 155.16 average IQ of the triple Niners (corresponding to an average ratio IQ of about 168) has to be a deviation IQ. To further muddy the waters, Dr. Hans Eysenck says of the adult Termites,

    "But it is with respect to intellectual ability that the group shines most brilliantly; on tests like the Concept Mastery Test specially devised for high-fliers, the majority scored close to the top percentile; if anything, they showed a gain in IQ over the period covered."
-----Genius, pg. 61

    Dr. Eysenck is saying that the Termites' IQs may have risen a little since childhood. Obviously, there is a rift within the lute here that demands resolution before continuing with this analysis.
    In 1940, deviation IQs didn't exist*. However, Dr. Terman and his associates would have been well aware of the disparities betweeen Gaussian predictions and the data they had amassed in their 1921 IQ assessment. I suppose it's possible that they normed the CMT on the basis of frequency data rather than mental ages, thereby anticipating what in the 1960's would be called deviation IQs. If this is the case, then the Termites adult CMT scores, cited in the sixth column of Table 4 above, would have been only a little less than their equivalent childhood deviation IQ scores. There would have been regression to the mean, but it wouldn't have been startling. On the other hand, if the CMT IQs were ratio IQs, then the regression to the mean was sizable, as Grady Towers describes above.

This may help explain why the Termites didn't necessarily set the world on fire. They were smart, but not that smart. The 26 adults who tested at or above 180 as children (with a corresponding average deviation IQ of, perhaps, 163) had dropped to an average score of, at a guess, 161 on the CMT, a drop of 2 points. However, if their average adult score of 161 on the CMT is a ratio-IQ score, they will have dropped to a deviation IQ of about 151—a decline of about 12 points of deviation IQ. They would have registered, perhaps, 20 to 25 points of IQ above the average Termite. That's still a significant difference, but considering the handicaps in interfacing with a society designed (from their perspective) by mental pygmies, it may not be surprising that there was no difference in worldly success. We know today that there's a "sweet spot" with deviation IQs ranging from about 120 to about 150 (ratio IQ of 160) in which IQs are sufficiently high to give their owners an edge, and yet not so high that they're at risk of being out of joint with the world.

    This result has two implications.
    First, if, on average, the Termites' IQs dropped significantly below the levels that would be expected in a population of 250,000—e. g., to the levels that would be expected in a population fo 100,000—then this would suggest that some of "late blooming" children who were missed in the 1921 screening later surpassed, in adulthood, some of the Termites. There should have been enough of these adults to account for the expected number of adult gifted in a population of 250,000. Presumably, the missing "late bloomers" would have fallen near the bottom of the range, since the numbers of Termites in the higher IQ ranges in childhood is approximately what would be expected based upon Vernon Sare's data. (In fact, if anything, there are more Termites in these ranges than would be predicted by the Vernon Sare study, due, perhaps, to the high fraction of children from professional families included in the study.)
    Second, with the adults who tested as children at or above a ratio IQ of 180, we're looking at a corresponding adult deviation IQ threshold of about 159, and an estimated average adult deviation iQ of 161. Then we're comparing these individuals with childhood ratio IQs above 180 with the average Termite, possessing an average adult IQ of, perhaps, 135. That's 26 points of IQ, but it's not an enormous difference.


* - The 1957 Form S version of the California Test of Mental Maturity (CTMM), and my early-60's copy of the Slossen Intelligence Test (SIT) are both ratio tests, and are predicated upon the mental age construct. The maximum mental age on the SIT is 27, and the corresponding ceiling on the CTMM is 32. Interestingly enough, the background material for the SIT assigns a rarity of 1 in 10,000 to an adult ratio IQ of 160, although as we've seen above, it must have been known from the time of the initial Terman screening of the 250,000 California schoolchildren in 1921 that the frequencies of occurrence of these ratio scores were far larger than is predicted by a Gaussian normal distribution.