Psychometric Questions
(1) The Flynn Effect
(a) Have IQ scores risen
linearly or exponentially (additively or multiplicatively)?
IQ scores
on the WAIS and S-B have been rising of the order of 3 points per
decade over at least the 83 years since 1918.Question: Has IQ risen additively,
climbing three points per decade by 25 points over this 83-year interval
(83 years X 0.3 IQ points/year) or has it risen exponentially (multiplicatively)
3 points per decade for a total of 28 points (e0.25)
over the interval? In other words, are these percentages additive or are
they multiplivcative? Presumably, they're multiplicative, since IQ tests
have been restandardized several times overthe 85-year period. Dr. James
Flynn's most recent paper quotes a 28-point rise since 1918, consistent
with the idea that the Flynn Effect increases are multiplicative. It could
fairly be argued that the changes aren't entirely regular or easy to measure,
and that a three-point difference is in the noise level. However, (a) the
cumulative effects may readily be measured by giving present-day test subjects
the 1916 Stanford Binet and the oldest versions of other IQ tests, and
(b) these disparities become more significant if we extend this 0.3% per
year rise in IQ back into the 19th century.
(c) Are we talking a
standard deviation of 15 or of 16 when we discuss the Flynn Effect?
The difference
is only 2 points at the 2-sigma level, but of course, it enlarges as we
deviate farther from the norm.
(b) An IQ gain of 25
points looking backward to 1916 translates into an IQ gain of 33 points
looking forward from 1916.
The average
citizen in 1916 might expect to rate an IQ
score of 75 on an IQ test normed in 2001. Conversely, today's average
citizens (IQ = 100) should earn about 133 (100/75 X 100) on the 1916 Stanford
Binet. However, the pre-1960 IQ scores were largely ratio IQ scores,
while scores today are deviation IQ scores. 25 points of deviation IQ represents
27 points of ratio IQ. Note the distinction between IQ changes viewed retrospectively,
and IQ changes viewed prospectively. If a mutual fund drops in value by
33%, it will have to rise 50% from its new, lower price to return to its
original price.
(c) Is this Flynn-Effect
shift in IQ a shift in deviation IQ or is it a shift in ratio IQ?
We know
something about the ratio-IQ distribution in 1918, 1921, and the 20's,
and 30's from the Terman
Study, from Leta Hollingworth's "Children
Above 180 IQ", from the Quiz
Kids in the 40's, and perhaps, from a review of the Army Alpha
Test results. One of the finds is that in these relatively small populations,
IQ's of 200 (based upon a standard deviation of 16, and generally measured
using the 1916 or 1937 S-B) were found with a frequency of about 1 in 500,000
rather than 1 in 5,000,000,000. All other IQ's at levels more than about
2 standard deviations above the mean were found with greater frequency
than a Gaussian distribution predicts. So when we get a 33-point shift
in average IQ, as seen prospectively from 1918, we're looking at a significant
difference between a 33-point increase in ratio IQ and a 33-point increase
in deviation IQ (equivalent to a 37-point delta in ratio IQ). And if we
examine the Flynn Effect upon IQ's even modestly above the mean--viz.,
a 2001 ratio IQ of 121 or a 2001 deviation IQ of 120--and we suppose that
this will translate into a 1916 S-B ratio IQ of 158 if the Flynn Effect
has acted upon mental ages, or a deviation IQ of 153 if the Flynn Effect
has acted upon deviation IQ's, these differences become quite significant.
The average proletarian today presumably earns a ratio IQ of 133 on the
1916 S-B, while the individual with a deviation IQ of 120 today would register
a ratio IQ of 153 or 157 on the 1916 S-B. Converting both scores to deviation
IQ's yields deviation IQ's of 130 and 145, or 148, respectively. This would
compress the Gaussian distribution of IQ's, pulling in its wings. On the
other hand, if the Flynn Effect has acted upon deviation IQ's, raising
them all by 37 points of 1918 ratio IQ or 33 points of 1918 deviation IQ
(standard deviation of 16, looking forward from 1918), then the Gaussian
would simply have been shifted to the right by 37? 33? points of IQ measured
on a 1918 scale, or 25 points of IQ measured with today's yardstick.
(c) How much of the Flynn
Effect is hollow with respect to g and how much is real?
How precocious
are children today? When do they start to speak? When do they start to
read? How does today's Gesell Development Guide compare with the same guide
in the 1930's? Have vocabulary, arithmetic, and general information increased
since 1918? Since 1950? How much?
(However, one confounding problem might be that many older IQ tests placed
a premium upon vocabulary, arithmetic, and general information, and this
has risen minmally over the past 85 years.)
(d) How were adult IQ
scores above 100 normed on older IQ tests that relied on mental age?
It seems
to me that they would either have to have been anchored to the projected
IQ's of adults whose childhood IQ's were known but which were subject to
regression to the mean and were not completely reliable, or they would
have to have been determined on a percentile basis, but for outliers, this
makes a big difference when it comes time to evaluate their scores.
There
would seem to me to be three problems with generating a mental age scale
for adults above the basal mental age (which was taken in those days to
be 16).
One would
be the problem of ceiling effects for raw scores above 90% correct out
of the total number of questions on the test. (In many cases, based upon
my own experience in administering IQ tests, it probably arises well below
that 90% level when someone is very strong in a particular area such as
spatial relations.) This 90% limit for many tests such as the Henmon Nelson
would seem to me to reduce the valid ceiling of the test from a mental
age of 24 to a mental age no greater than 20.5, corresponding to an adult
ratio IQ of 128. The test-taker must answer 81 questions correctly out
of 90 to earn a mental age of 20.5. So for practical purposes, the reliable
ceiling on the Henmon Nelson would seem to me to be no greater than an
adult IQ of 128. For the California Test of Mental Maturity, with 145 questions
and a mental age ceiling of 32, the effective ceiling is 25.6 years of
mental age, corresponding to an adult ratio IQ of 160.
The second
problem would have been the possible discrepencies between a Gaussian distribution
and the actual distribution of adult intelligence. Up to an adult IQ of
125, we could probably assume, based upon the situation with childhood
IQ's, that there is no more than a difference of the order of one-point
between a normal distribution and the actual, observed upper-half distribution
of IQ's. However, above that range, the discrepencies accelerate. Consequently,
percentiles would have afforded a reliable ratio IQ yardstick up to about
the 94th percentile (adding one point to the derived ratio IQ to allow
for the ~1 point discrepency between ratio IQ's and deviation IQ's).
The third
problem would have been that childhood IQ's couldn't have been used very
reliably to estimate adult mental ages because they often change by some
number of points as the child matures.
So how
did the designers of those old IQ tests arrive at an adult mental age scale?
One way to aproach it might have been to have established reliable mental
ages for the IQ range between 75 and 125 by using percentiles and generating
deviation IQ's, which, as I've argued, will probably be within about about
a point of each other. I can probably add a point and assign a ratio IQ
of 126 and a mental age of 20 yrs., 2 months to someone who scores at the
94th %tile (deviation IQ = 125). Then to arrive at a mental age of 24 to
establish the ceiling of the test, I might be able to utilize the adult
scores of test subjects who earned a mental ages approximating 20 years
when they were 13 years, 4 months, for IQ scores of 150 on a test with
a ceiling (for that age) of 180. This presumably gives them enough headroom
to avoid ceiling effects. If I assume no decline in IQ between 13 years,
4 months, and 16 years of chronological age, then I can use these individuals
to help benchmark my adult test. However, there still remains the influence
of ceiling effects upon these "benchmarkers". As 16-year-olds, they probably
aren't all going to make perfect scores on the Henmon Nelson test. None
of them can earn scores that are greater than perfect, and if some
of them make scores that are less than perfect, they'll drag down the average
mental age for the group, since 24 (corresponding to an adult IQ of 150)
is the highest mental age anyone can earn.
???
(e) What kind of score
does today's average child make on the 1916 Stanford Binet?
The Army
Alpha and Beta tests? The Thorndike CAVD? How about above-average children?
What about average adults? What's the shape of the curve(s)? What studies
have been run, and by whom?
(f) Has the Flynn Effect
boosted IQ's in proportion to their values?
If someone
has a ratio IQ of 200, is the Flynn Effect twice as great for them as it
is for an IQ of 100? If not, then the distribution of IQ's would have to
have changed since 1918. It has been mentioned that the Flynn Effect acts
primarily upon those whose IQ's lie close to the mean.
Case I: No, or minimal Flynn Effect at the upper end of the IQ spectrum
To show what this would mean, let's suppose that the Flynn Effect has had
no effect upon upon individuals with deviation IQ's of 143. (In reality,
it would probably be a sharply reduced effect but it probably wouldn't
be zero. But I have an explanatory motive in selecting that IQ of 143,
and in setting its Flynn Effect equal to zero.) Now suppose that a group
of present-day 6-year-olds with an average IQ of approximately 100 takes
the 1916 Stanford-Binet. They would presumably earn an average score of
~133 on that test, corresponding to a mental age of about 8. Another group
of 6-year-olds with present-day deviation IQ's clustered around 143 also
takes the 1916 S-B. Since a deviation IQ of 143 corresponds to a ratio
IQ of 150, and since the Flynn Effect is presumed to have had no effect
on IQ's in this upper register, they would be expected to average 150 on
the 1916 S-B, just as they would on the 1973 Revision of the S-B. Thus,
they would have a mental age of 9, only 12.5% higher than the children
with a present-day IQ of 100. In other words, the entire present-day distribution
of IQ's between IQ 100 and a present-day deviation IQ of 143, or a ratio
IQ of 150 on the forthcoming Fifth Revision of the Stanford Binet, would
be squeezed into the range from 133 to 150 on the 1916 test. The implication
would be that today's individual with a deviation IQ of 143, instead of
being "50% smarter" or "43% smarter" than today's average channel surfer
would only be "12.5% smarter". Our present-day tests wouldn't necessarily
reveal this because they're based strictly upon percentiles. But that would
mean that enormous distortions have occurred in the distribution of intelligence
since 1916. It would no longer be even remotely Gaussian.
Case 2: The same Flynn Effect for all IQ's
Suppose that the Flynn Effect is the same 3 points per decade for all IQ's.
Obviously, we have a problem at the bottom of the bell curve, where the
lowest possible IQ is now 33, measured on the 1916 S-B, or 25 measured
on present tests. Now let's return to our example of a cohort of today's
children with an IQ averaging 100, and a cohort of today's children
with a ratio IQ averaging 150, (deviation IQ of 143). On the 1916 S-B test,
today's average child would score 133, as before, and today's child with
a ratio IQ of 150 would score 183.The ratio of 183 to 133 is about 1.376,
or less than today's 150/100 ratio of ratio IQ's (or 143/100 for deviation
IQ's). The distribution function would have become compressed and distorted,
but not nearly as much as it was in Case 1.
Case 3: A Flynn Effect that's proportional to
the IQ
In this case, the child with a present-day deviation IQ of 143 or a present-day
ratio IQ of 150 would hav experienced a Flynn Effect rise since 1916 of
33 X 1.5 = 49.5 (as measured on the 1916 S-B test, and would be expected
to score ~199.5 on that test. In this case, the shape of the curve is preserved
as we transition from 1916 to the present time. The only sticking point
arises, as it did for Dr. Flynn, when we try to reconcile someone like
Carl Friedruch Gauss, who learned to read at 2 and corrected his father's
arithmetic before he was 3, with the reduced IQ that we must assign to
him by virtue of a Flynn Effect that wouldn't allow him a current ratio
IQ greater than 150, and a current deviation IQ greater than 143!
(g) Does
a lifetime of intellectual exercise in an increasingly complex world lead
to Flynn Effect boosts for the elderly? Are we keeping up with the times?
There is evidence that indicates that part of the age-related cognitive
decline that we've attributed to the elderly is a manifestation of the
Flynn Effect. IQ tests have gotten tougher, but one's IQ seems to be frozen
at the level of one's youth, particularly on tests of fluid g. One way
to examine age related cognitive decline might be through the age corrections
for WAIS scores.
Using
the coefficients in the table, I've calculated below the maximum WAIS IQ
score for the various age ranges. What's shocking about this is the age-related
cognitive decline as we go from 25-29 to 75-79. We might expect a Flynn-Effect
decline over the 50-year period of 15 points of iQ, but instead, we find
a 45-point decline in absolute scores, which I'll take as a proxy for IQ.
The average 75+-year-old will score only 60.5% as well, in terms of absolute
scores, as the average 25-29-year-old. Only the top 2% of 75+-year-olds
will match the average 25-29-year-old on an absolute basis. Someone with
a 160 IQ at 25-29 will have fallen back to a 125 IQ measured without age
correction by age 75+.
Age 16-17: Mean 103.7 SD
23.61 = 161.18
Age 18-19: Mean 106.74 SD
25.16 = 155.6
Age 20-24: Mean 110.10 SD
25.69 = 152.49
Age 25-29: Mean 113.55 SD
24.98 = 151.91
Age 30-34: Mean 107.09 SD
24.30 = 157.35
Age 35-39: Mean 108.77 SD
25.06 = 154.65
Age 40-44: Mean 103.17 SD
24.04 = 160.42
Age 45-49: Mean 101.53 SD
27.04 = 154,62
Age 50-54: Mean 95.99 SD
24.73 = 163,31
Age 55-59: Mean 92.83 SD
26.27 = 161.19
Age 60-64: Mean 90.21 SD
24.15 = 168.19
Age 65-69: Mean 88.13 SD
22.92 = 172.21
Age 70-74: Mean 77.19 SD
21.42 = 186
Age 75+:
Mean 68.71 SD 21.56 = 191.34
Equally intriguing are the changes going from age 16 to age 25-29. On older IQ tests, it was assumed that the IQ didn't change beyond the age of 16. This table shows that it increases almost 10%, peaking at age 25-29. If we subtract 3 points going from 16-17 to 26-27 to correct for the Flynn Effect, then it differs by about 13%.
This second table attempts to show how the IQ varies with age after correcting for the Flynn Effect (assuming the usual three-points-per-decade rate of change for the Flynn Effect). Obviously, there's a lot more going on than the Flynn Effect.
Age 16-17: Mean 100.7 SD
23.61
Age 18-19: Mean 103.74 SD
25.16
Age 20-24: Mean 111.60 SD
25.69
Age 25-29: Mean 113.55 SD
24.98
Age 30-34: Mean 108.59 SD
24.30
Age 35-39: Mean 111.77 SD
25.06
Age 40-44: Mean 107.67 SD
24.04
Age 45-49: Mean 107.53 SD
27.04
Age 50-54: Mean 103.49 SD
24.73
Age 55-59: Mean 101.83 SD
26.27
Age 60-64: Mean 100.71 SD
24.15
Age 65-69: Mean 100.13 SD
22.92
Age 70-74: Mean
90.59 SD 21.42
Age 75+:
Mean 83.71 SD 21.56
(2) How do various capabilities
scale with IQ? With mental age? (I'm looking for absolute measures of intelligence.)
Why are
IQ's measured only on relative scales? Why aren't they measured in absolute
terms? Saying that someone is brighter than than 99% of the population
is no more meaningful than saying that someone is taller than 99% of the
population.
(4) Miscellaneous Questions
Adult AGCT IQ vs. Deviation
IQ
|
AGCT IQ
|
Deviation IQ
|
1 in (see below)
|
Cum.# in 2,400,000
|
# of Ph. D.'s
|
Phys. Sci | ||
| 170+ | 156.5+ | 1-in-4,500 |
530
|
46
|
43% | ||
| 160+ | 148+ | 1-in-750 |
3,200
|
147
|
46% | ||
| 150+ | 140+ | 1-in-156 | 15,350 | 484 | 45% | ||
| 140+ | 132+ | 1-in-44 | 54,600 | 1,014 | 46% | ||
| 130+ | 124+ | 1-in-14.76 | 162,600 | 1,840 | 36% | ||
| 120+ | 116+ | 1-in-6.3 | 380,800 | 2,646 | 30% | ||
| 110+ | 108+ | 3.2 | 742,600 | 3,166 | 27% | ||
| 100+ | 100+ | 2 | 1,200,000 | 3,464 | 21% | ||
| 100- | 92- | 2 | 1,657,400 | 3,545 | 23% | ||
| 90- | 84- | 3.2 | 2,019,200 | 3,560 | 20% | ||
| 80- | 76- | 6.3 | 2,237,400 | 3,567 | 14% | ||
| 2,400,000 | 3,567 |
5. The Very Brightest and
Their Relationships with the World