A. THE DEFINITION.
In order to direct attention to the quantitative description of
intellectual deficiency which is here proposed, let us state the
percentage definition in its most general form. _Individuals whose
mental development tests in the lowest X per cent. of the population
are_ PRESUMABLY INTELLECTUALLY DEFICIENT, _unless their deficiency is
caused by removable handicaps_. Above these is a group of Y per cent.
within which the diagnosis of intellectual deficiency is uncertain on
the basis of our present tests. The size of the presumably deficient X
group is to be determined by the number of intellectually weak which
society is at present justified in indefinitely isolating. The
doubtfully deficient Y group should include all those who are so
intellectually deficient as to be expected to need assistance
indefinitely. _The feeble-minded, or_ MENTALLY DEFICIENT, _are those who
require social care indefinitely because of deficiency in mental
development_. They include the X group, that portion of the doubtful Y
group which is found to require isolation, guardianship or social
assistance, and any others not detected by the tests but requiring
prolonged social care on account of their failure to develop mentally.
Under the principle which we stated at the close of the last section the
combination of Y ability and persistent serious delinquency brings the
case within the group presumed to be feeble-minded.
Besides the greater definiteness and significance of such a definition
of intellectual deficiency, it affords the simplest practical criterion
for determining the borderline of passable intellects with a scale of
mental tests. A detailed comparison of the percentage plan with other
forms of quantitative definition will be found in Part Two. We may note
here, however, that it guards against a number of the absurdities of
current descriptions of the borderline with measuring scales. It is a
criterion which may be consistently applied to the borderline of both
the immature and the mature. It may be adapted with comparative ease to
any system of tests. It aids in comparing the frequency of intellectual
deficiency among different groups, for example, among different types of
delinquents, regardless of whether the investigators have used the same
series of tests, provided only that each series has been standardized
for similar random groups.
Any form of quantitative definition, on the other hand, involves certain
assumptions which must be defended before it can claim to be of
advantage for practical purposes.
B. THE ASSUMPTIONS OF A QUANTITATIVE DEFINITION.
(a) DEFICIENCY IS A DIFFERENCE IN DEGREE NOT IN KIND.
Fortunately the tendency to describe the feeble-minded person as if he
were a different species from the normal has been definitely attacked by
two noteworthy researches, that of Norsworthy (_159_) and that of
Pearson and Jaederholm (_164_) (_167_). In these two investigations
mentally deficient children either in special classes or in institutions
have been compared with groups of normal children from the same
localities on the basis of objective tests. The results are uniformly
supported by numerous other studies of deficient and normal groups with
the Binet and other tests. The conclusion is, therefore, thoroughly
established that there is no break in the continuity of mental ability.
It grades off gradually from average ability, and continually fewer and
fewer individuals are to be found at each lower degree of ability. The
borderline of deficiency will, therefore, not be a mental condition
which clearly separates different kinds of ability, but a limiting
degree of capacity to be decided upon by social policy in attempting to
care for those who most need social guardianship. Since ability changes
gradually in degree it is necessary to indicate a doubtful border region
of degrees of ability on which expert judgment must supplement the test
diagnosis. Below the doubtful region the diagnosis is clearly supported
by objective test criteria, so that the only question to raise is
whether the condition is caused by removable handicaps. The percentage
definition thus strictly conforms to the best objective studies of
mental deficiency in treating deficiency as a difference in degree.
It should, perhaps, be said that this view is in direct conflict with
the opinion that mental deficiency is accounted for as a Mendelian
_simple unit_ character. The opposing view has been advocated by
Davenport (_95_, p. 310) and others in the publications of the Eugenics
Record Office, and accepted by Goddard (_112_, p. 556). It has been so
fully answered by Pearson (_164_) and Heron of the Galton Laboratory
(_127_) and by Thorndike (_198_) that there is no occasion to take up
the question in detail. We seem to be reaching an understanding so far
as our present problem is concerned. If the explanation of the
inheritance of mental ability is through Mendelian characters,
nevertheless intellectual ability is the result of such a complex
combination of units that it may best be thought of in connection with
the unimodal distribution of ability adopted in this study. No random
measurement of mental ability has ever shown any other form of
distribution.
The attempt has also been made by Schmidt (_179_) to find qualitative
differences between normal and feeble-minded children by means of tests,
and by Louise and George Ordahl (_162_) to find qualitative differences
between levels of intelligence among feeble-minded children. While these
studies are very suggestive in pointing out the tests which most clearly
indicate differences between individuals, they seem to me to fall far
short of showing that the qualitative distinctions are anything more
than larger quantitative distinctions. It is not clear that the authors
intended them to mean anything more than this, so these studies do not
seem to conflict seriously with our assumption that intellectual ability
grades off gradually and uninterruptedly from medium ability to that of
the lowest idiot.
(b) AS TO THE VARIATION IN THE FREQUENCY OF DEFICIENCY AT DIFFERENT
AGES.
A quantitative definition of intellectual deficiency would certainly be
much simpler if it could be assumed that the percentage of deficients at
each age is practically constant during the time when a diagnosis of
deficiency is most important, say from 5 to 25 years. Otherwise the
objection might be raised that it is impracticable to determine
different percentages for each year of immaturity or to formulate our
borderlines of ability for a particular age. When the general
instinctive origin of intellectual deficiency is considered along with
the incurability of the condition, we seem to be theoretically justified
in assuming that the variation will be slight from one year of life to
the next. This assumption is tacitly made by all those who use Stern's
quantitative description of deficiency in terms of the mental quotient.
On the other hand, there is a feeling among some of the investigators
that there is a sudden influx of feeble-minded at particular ages and
this position should be examined. Probably more important than this
possibility of increase is the question of a decrease in frequency with
age on account of the excessive death rate among the deficients.
It is a natural supposition that there is a sudden increase in the
proportion of feeble-minded at adolescence. On account of the increased
rate of growth at this period we might expect to find greater
instability for a few years. It may well be that there is a rather
sudden influx of the unstable type of feeble-mindedness at this period.
Such an increase may occur without being detected by a series of brief
intellectual tests such as the Binet scale. It would be of the conative
type of feeble-mindedness that cannot at present be diagnosed by
objective tests, the type that requires diagnosis by expert opinion. It
is to be noted, however, that Binet, who paid much attention to the
unstable type, says: “Since the ill-balanced are so numerous at ten
years of age, and even at eight, we conclude that in many cases the
mental instability is not the result of the perturbation which precedes
puberty. This physiological explanation is not of such general
application as is sometimes supposed” (_77_, p. 18).
Only when an emotional disturbance is so great as to be detectable by
mental tests will this influx need to be taken into consideration in
stating the borderline for objective tests. The evidence that few cases
of feeble-mindedness are not detectable until after ten years of age is
all the other way. With the Stanford measuring scale, Terman and his
co-workers did not even find a noticeable increase in the variability of
the groups at the ages of adolescence (_57_, p. 555). It is to be
remembered also that we are not concerned here with mere instability
which corrects itself with more maturity, such as has been described by
Bronner among delinquents. This does not, of course, amount to an
incurable conative deficiency and is not classified under
feeble-mindedness.
Goddard has suggested that possibly the moral imbecile group comes into
our class of feeble-minded suddenly with a common arrest of development
at about the stage reached by the nine-year-old. He notes that “of the
twenty-three cases of this sort picked out for us (at Vineland) by the
head of the school department, fifteen are in the nine-year-old group,
five in the ten-year-old, two in the eleven, and one in the twelve”
(_113_). He regards this evidence, however, as meager and only
suggestive. Doll has given evidence of late appearance of retardation in
rare cases (_100_ and _99_).
It is to be noted that if a sudden change is found in the percentage of
children falling below a certain test standard it is perhaps more likely
to mean that there is a change in the difficulty of the tests at that
point. For example our Table V shows 1.3% of the nine-year-olds test two
or more years retarded, while 18.9% of the ten-year-olds are retarded
two years or more. This presumably indicates a change in the relative
difficulty of the tests for VII and VIII rather than a change in the
frequency of retardation at ages nine and ten. When we turn to Goddard's
norms for VII and VIII we find that 81% of the seven-year-old children
pass the norm for VII while only 56% of the eight-year-old children pass
the norm for VIII.
The Jaederholm data (_167_) obtained by applying the Binet tests to
pupils in the regular school classes and in special classes for the
retarded may suggest a possible influx of intellectual deficiency at
about 12 years of age or else “more mental stagnation in the
intellectually defective” at this life-age and after. If one were to
define intellectual deficiency in terms of the standard deviation of the
regular school children, this data suggests that there is a marked
increase in the number of children sent to the special classes at 12
years of age who are -4 S. D. or lower. Roughly speaking it amounts to
36 children at 12 years of age, 36 at 13, and 21 at 14, as compared with
11 at 11 years and 13 at 10 years. On the other hand, this may as well
mean that intellectual deficiency becomes greater in degree rather than
in frequency at these ages. The latter interpretation is adopted by
Pearson for the Jaederholm data, so that it is perhaps not necessary to
consider this evidence further. On the average the pupils in the special
classes fall about .3 S. D. months further behind regular school
children with each added year of life from 5 to 14 inclusive. A third
possible interpretation of the greater number showing the degree of
deficiency measured by -4 S. D. with the older ages should be mentioned.
It is possible that 1 S. D. has not the same significance for
5-year-olds as for 12-year-olds. The distribution of abilities at
succeeding ages may be progressively more and more skewed in the
direction of deficiency. We shall return to this point in Part Two as
showing the advantage of the percentage definition over a definition in
terms of the deviation. In connection with the Jaederholm data on
special classes one should also consider the fact that younger children
are not as likely to be detected by the teachers and sent to the special
classes. It is possible also that the difference in difficulty of the
tests for different age groups is somewhat obscured by using a year of
excess or deficiency as a constant unit as Pearson has in treating this
data. The bearing of this difference in difficulty was pointed out above
for Goddard's data.
The investigations by Pearson of children in the regular school classes
indicate that there is no important shift with maturity in the frequency
of those with different degrees of ability, when the ability is measured
either in terms of years of excess or deficiency with the Jaederholm
form of the Binet scale or in terms of estimates of ability relative to
children of the same age (_166_ and _167_). In both these studies the
correlation of ability with age was shown to be almost zero. For tested
ability for 261 school children “r” was .0105, P. E. .0417; with the
estimated ability, the correlation ratios were for 2389 boys, .054, P.
E. .014; for 2249 girls, .081, P. E. .014. Until we have better data
this is certainly the most authoritative quantitative answer to the
question of the shift with age in the frequency of the same relative
degree of mental capacity.
The best method of empirically settling this question of the early
appearance and constancy of deficiency would be to test the same group
of children again after they had reached maturity and find out how many
of those who tested in the lowest X per cent. still remained in the same
relative position. This is, of course, not possible at present, but it
certainly should be done before we are dogmatic as to the permanent
isolation of the lowest X percentage at any age. The nearest approach to
this sort of evidence is Goddard's three annual testings of a group of
346 feeble-minded children with the Binet scale (_117_, p. 121-131).
Among these 109 showed no variation, 123 gained or lost 0.1 or 0.2 year,
18 lost 0.3 or more, and only 96 gained 0.3 or more of a year. With so
small a change in absolute tested ability the probability of a change in
position relative to normal children seems to be slight. Only one of the
76 who had tested in the idiot group gained as much as a half year in
tested age in three years.
It is not possible to settle this question of the constancy of the
percentage of intellectual deficiency from one life-age to the next by
considering the frequency of different ages of children among those who
are sent to special classes for retarded pupils. This is evident from
the fact that these classes contain a considerable proportion of those
who are feeble mentally mainly because of conative disturbances. These
would not be detected by our present tests and would not be classed as
_intellectually deficient_. In the second place the pupils for the
special classes are usually selected mainly on the advice of their
teachers, who cannot, of course, without tests select those who are
intellectually deficient except by trying them for a number of years in
the regular school classes. This means that a smaller percentage of
pupils in the special classes at the younger ages is to be expected.
The figures of the U.S. Census as to the ages of inmates of the
institutions for feeble-minded are also of little significance in
connection with the question of the variation from age to age. That the
number of inmates at the different ages is affected most largely by the
pressure of necessity for shifting the care from their homes to the
institution is shown by the fact that three-fourths of the admissions
are of persons over 10 years of age. It is also indicated by the fact
that for the period from 15 to 19 the males are over 20% more frequent
than females, while from 30-34 the females are nearly 20% more frequent.
Considering those ages most frequently represented in the institutions,
10-24 years, the average variation for the three five-year periods in
the percentage of the population of the corresponding ages who are in
these institutions is only 0.01%. The middle five-year period has the
most, but even if there were a cumulation of feeble-mindedness with age,
which is not shown, we would anticipate a change of not more than 0.05%
for these 15 years. This would be clearly negligible in considering the
general problem.
That little allowance for the variation from age to age need be made for
the number of cases not discoverable at the beginning of school life is
further indicated by report of the Minnesota State School for
Feeble-Minded. It shows that in only 247 out of its 3040 admissions was
the mental deficiency known to commence after six years of age (_154_).
If the number of feeble-minded who should be isolated were found to
increase after school age less than one in 10,000 of the population, as
this suggests, it would surely be better to neglect this variation from
age to age than to emphasize it in dealing with the problem of objective
diagnosis and social welfare.
How rare is the onset of feeble-mindedness after five years of age is
also shown by the frequency of hereditary causes. In his study of the
300 families represented at Vineland, Goddard places only 19% in his
“accidental” group and 2.6% in the group for which the causes are
unassigned. The rest are either in the hereditary group, probably
hereditary, or with neurotic heredity. Half of the cases in the
“accidental” group are due to meningitis. His histories show that only 9
of the “accidental” and unassigned groups were unknown at 5 years of
age. This is only 3% of his total feeble-minded group. To these might be
added, perhaps, a few from the hereditary groups who did not show their
feeble-mindedness at so early an age, but so far as I can judge these
would not be of the intellectually deficient type that would be
detectable by the Binet scale at any age. They would test high enough
intellectually to pass socially and require expert diagnosis to be
classed as feeble-minded.
Certain diseases, epilepsy and meningitis, are undoubtedly causes of
feeble-mindedness. The evidence, however, seems to be that they are so
rare compared with the mass of mental deficiency that after 5 years they
may well be offset by the excessive death rate among the feeble-minded.
That recoveries from feeble-mindedness are insignificant is generally
agreed. Among the 20,000 in institutions in 1910 only 55 were returned
to the custody of themselves. This is further evidence of the
fundamental, if not congenital, nature of the deficiency.
While the evidence submitted above makes it seem fair to assume that the
increase in the frequency of a certain degree of intellectual deficiency
with age is probably negligible, it is not clear that the decrease with
age in the proportion of feeble-minded caused by an excessive death rate
may be neglected even for the test ages 5 to 25. By searching the
literature it has been possible to assemble the records for nearly 3500
deaths among the feeble-minded in institutions in this country and Great
Britain distributed by ages in ten-year periods. This evidence is
presented in Table I. The number of cases under five years of age living
in the institutions is so small that the deaths under five years are
certainly misleading. They have, therefore, been omitted from the table
and the distribution calculated for those five years or over (_123_,
_154_, _204_, _205_). Comparison is made with a similar distribution of
the total deaths for a period of five years from 1901 to 1904,
inclusive, within the area of the United States in which deaths are
registered, compiled from the special mortality report of the Bureau of
the Census (_206_). This registration area has a population of about
32,000,000. The general agreement of the distribution of deaths among
the four different groups of institutional inmates seems to make it
reasonable to assume that the United States group of institutional
deaths for the year 1910 is a conservative description of excessive
death frequency at the early ages among the feeble-minded in
institutions.
TABLE I. _Age Distribution of Deaths in the General Population and Among
Feeble-Minded in Institutions._
────────────┬──────────┬───────────────────────────────────────────────
│Population│ Ages
────────────┼──────────┼───────┬───────┬───────┬───────┬───────┬───────
│ │ 5-14 │ 15-24 │ 25-34 │ 35-44 │ 45-54 │ 55 &
│ │ │ │ │ │ │ over
────────────┼──────────┼───────┼───────┼───────┼───────┼───────┼───────
Gen'l—U. S. │ 1,897,492│ 6.1% │ 9.6% │ 12.8% │ 13.0% │ 13.6% │ 44.9%
in death │ │ │ │ │ │ │
registration│ │ │ │ │ │ │
area │ │ │ │ │ │ │
────────────┼──────────┼───────┼───────┼───────┼───────┼───────┼───────
F. M. 1910 │ 840│ 26.6 │ 33.0 │ 18.9 │ 9.1 │ 45 & │
in │ │ │ │ │ │ over │
Institut'ns │ │ │ │ │ │ 12.3 │
in U. S. │ │ │ │ │ │ │
────────────┼──────────┼───────┼───────┼───────┼───────┼───────┼───────
F. M. │ 997│ 34.3 │ 41.1 │ 10.4 │ 6.5 │ 3.5 │ 55 &
British │ │ │ │ │ │ │ over
(Earlswood) │ │ │ │ │ │ │ 4.2
────────────┼──────────┼───────┼───────┼───────┼───────┼───────┼───────
F. M. │ 613│ 34.7 │ 46.8 │ 9.5 │ │ 35 & │
British │ │ │ │ │ │ over │
(Barr) │ │ │ │ │ │ 9.0 │
────────────┼──────────┼───────┼───────┼───────┼───────┼───────┼───────
F. M. │ 982│ 27.6 │ 38.0 │ 16.1 │ 8.6 │ 3.5 │ 55 &
Faribault │ │ │ │ │ │ │ over
Minnesota │ │ │ │ │ │ │ 6.2
────────────┴──────────┴───────┴───────┴───────┴───────┴───────┴───────
TABLE II. _Mortality of Institutional Deficients in the United States
Compared with the General Population, Showing its Possible Effect on the
Frequency of Deficiency at Different Ages._
Ages
───────────────────────────────┬────┬────┬────┬────┬────┬────┬────┬────
│ 5 │ 10 │ 15 │ 20 │ 25 │ 30 │ 35 │ 40
───────────────────────────────┼────┼────┼────┼────┼────┼────┼────┼────
General population │1000│983 │972 │956 │934 │903 │872 │835
───────────────────────────────┼────┼────┼────┼────┼────┼────┼────┼────
Deficients in Institut'ns │1000│795 │696 │606 │503 │428 │349 │290
───────────────────────────────┼────┼────┼────┼────┼────┼────┼────┼────
│ │ │ │ │ │ │ │
Per cent. deficient if 1% at │1.40│1.11│1.00│ │.75 │ │ │
age 15 │ │ │ │ │ │ │ │
───────────────────────────────┴────┴────┴────┴────┴────┴────┴────┴────
[Illustration: FIG. 1. _Mortality among Feeble-Minded in Institutions
Compared With the General Population_]
A comparison of the death rates of the feeble-minded and the general
population at different ages is of prime importance in connection with
all attempts at quantitative descriptions of deficiency. Heretofore this
has been completely neglected. Fig. 1 and Table II have been prepared to
provide a roughly adequate estimate, on the basis of the above data for
the United States, as to the survival of 1000 institutional cases of
feeble-minded 5 years of age for successive age periods compared with
1000 people in the general population. In constructing this table it was
necessary to assume, since the facts were not given, that the age
distribution in the registration area of the general population was the
same as for the United States as a whole (census of 1910) and that the
number of feeble-minded in the institutions at the various age periods
was equal to the number enumerated on the first of January plus the
admissions during the year 1910, disregarding the number discharged
since they are not distributed by ages. The average annual death rate
among the institutional cases of feeble-minded 5 years of age and over
in the United States in 1910 was 35.19 per thousand, while the
corresponding death rate in the general population of the registration
area for the five years 1901-1904 inclusive was 13.56. Assuming that the
death rates are uniform within the five-year periods, the decline in the
proportion of institutional feeble-minded from 5-25 years of age as the
result of excessive mortality is indicated by the last line in Table II,
after allowing for the mortality in the general population. That this
effect of excessive mortality upon the percentage of feeble-minded
cannot be neglected between 5 and 25 years of age is apparent unless the
mortality among institutional cases is much greater than it is among the
deficient generally. As the figures stand the proportion of
feeble-minded would be reduced nearly one-half between ages 5 and 25.
Only a small part of this reduction probably would be compensated for by
new cases developing from accident or disease. On the other hand there
is little doubt that the institutions contain an excessive proportion of
low grade cases among whom the mortality is much greater. The mortality
among institutional cases is, therefore, probably not typical of that
among the feeble-minded generally. Nevertheless it is so great that any
quantitative definition of deficiency which neglects it entirely is open
to serious objection. We shall, therefore, keep this variation in mind
in connection with the discussion in the next chapter of the percentage
which is deficient, and in the adaptation of the definition to a
measuring scale. It is clear that the percentage should be so chosen as
to allow best for the possible large effect of excessive mortality among
the deficients. Finally, it should be said that the percentage
definition of feeble-mindedness might be modified to meet a varying
percentage from age to age should that ever become desirable.
(c) AS TO THE NUMBER OF DEFICIENTS NOT DETECTED BY TESTS.
If most of the feeble-minded for whom society should provide were of the
type which is only conative and not detectable by our present objective
tests, a quantitative definition would be abortive. We must, therefore,
study our assumption that it is worth while to direct our attention to
those who are intellectually deficient. We shall attempt to discover how
frequent are the primarily conative types.
Before examining the quantitative evidence we may note that it is in
conformity with two prominent recent tendencies in psychology to
subordinate specialized abilities, as compared with abilities which
function commonly in many situations. The first of these tendencies is
represented by the fundamental researches of Hart and Spearman (_123_)
(_185_). This is not the place to set forth the technical work on which
their conclusions are based. It may be said, however, that, with 17
different psychological tests, they were unable to discover any
important specific mental weakness which distinguished adults who were
suffering with any one of various mental abnormalities, including
imbecility, manic-depressive insanity, dementia praecox, paranoia, and
general paralysis of the insane. This may have been the fault of the
tests, but it seems to be more likely that the fault lies in the custom
of emphasizing special abilities and disabilities, at least from the
point of view of tested capacities. On the other hand, all of these
mental abnormalities showed a weakness in general intellectual ability.
This is true whether this general ability be regarded, as it is by Hart
and Spearman, as due to a general fund of brain energy, or whether
general ability be taken to refer to the common recurrence of many
specific abilities in much of our mental life. Its significance for this
study is that a series of varied tests, such as that of Binet, may be
expected to give a good estimate of general ability, and its failure to
disclose specific disabilities is thus less important.
The second influence in psychology tending to emphasize average tested
ability is the establishment of the biological conception of the mind
which recognizes the mutual interdependence of the mental processes,
organically united through the activity of the brain. So long as
intellectual, emotional and volitional processes are all mutually
dependent, a disturbance of one aspect of mental life is bound to affect
the others. In considering the mutual dependence of the mental
processes, it is important to weigh carefully the striking examples
which Bronner[4] has brought together, illustrating special abilities
and disabilities. She has made an admirable start toward a differential
diagnosis of special defects in number work, language ability and other
mental activities. The degree of special deficiency which results in
social failure could be placed upon an objective basis, but the rarity
of special deficiencies as compared with general deficiency will make
this a slow task. In the meantime we may rely upon the mutual dependence
of the organic processes as a point of view which emphasizes the common
spread of deficiency to many activities. Knowledge of a single case of
specific disability is sufficient to make us recognize that such cases
do occur. On account of the rarity of those cases and the absence of
objective criteria, it seems necessary to leave the further
differentiation to the future, considering here only those cases which
may be grouped together as conative, as contrasted with those detected
by our general intellectual tests.
Whether the group of primarily conative cases is of any considerable
size can be only very roughly estimated at present, since the diagnosis
of such cases of feeble-mindedness rests at present almost exclusively
on the subjective opinion of the examiner. Before their diagnosis is put
upon an objective basis we must have a different form of test directed
at such traits of will as initiative, perseverance, stability and
self-control. These probably center on the mental side around the
instinctive emotional background of interest and the passions, while, on
the physical side, they raise the question whether the subject's energy
is adequate to endure the strain of competition or whether it shows
itself only in sudden bursts.
If the diagnosis of conative cases could be determined objectively, it
is possible that most forms of social unfitness would be found highly
correlated with intellectual deficiency. On the other hand, when the
diagnosis of unfitness for school or social life depends merely upon the
opinion of experts or teachers, the inaccuracy of the diagnosis may show
a wide discrepancy between the so-called conative and intellectual types
of deficiency. Binet, on the basis of his acquaintance with the pupils
in special classes, suggested that the number of unstable children is
probably equal to the number of those who are intellectually unsuited
for the ordinary schools or institutions (_77_). Since he then places
the total number of the two classes at four or five per cent., it is
apparent that he is discussing a higher type of ability than is usually
included under the term feeble-minded. We can get somewhat better
evidence on this question by studying the results of Binet tests applied
to children cared for in special classes or in institutions for the
feeble-minded. Chotzen (90) presents a table of 280 children in the
_Hilfsschule_ in Breslau, only 201 of whom, however, he himself
diagnosed as feeble-minded, _i. e._, _debile_ or lower. Of these only 51
were intellectually deficient as indicated by the Binet tests when we
include the doubtful cases according to the criteria we have adopted in
this study. If we suppose that, in addition to those in the special
classes, there would be one intellectually deficient child in an
institution for feeble-minded for every child testing deficient, we
would then guess that only 40% of the feeble-minded children in Breslau
were intellectually deficient. This sort of estimate seems to agree with
Binet's belief that half of the children requiring special care, at
least during school ages, are cases which are primarily conative.
Pearson has approached the same problem in another way (_164_) (_167_).
He has used the results of the psychological tests applied by Norsworthy
to children in New York in special classes and institutions for
feeble-minded compared with those in the regular school classes, and the
results of Jaederholm obtained with the Binet tests applied to 301
children in Stockholm in the special classes compared with 261 others
selected from the regular classes. He found that “70.5% of normal
children fall into the range of intelligence of the so-called mentally
defective; and 60.5% of so-called mentally defective children have an
intelligence comparable with that of some normal children” (_167_, p.
23). On the statistical assumption that those in the normal classes
would distribute according to the Gaussian normal probability curve he
estimates that, with the Binet tests, among those in the special classes
“10% to 20%, or those from 4 to 4.5 years and beyond of mental defect,
could not be matched at all from 27,000 children” (_164_, p. 46).
Another 20 to 30% could be intellectually matched by those in the
regular classes having from 3 to 4.5 years of mental deficiency, but
they would be matched very rarely. On the assumption that 1% of the
children were feeble-minded, not more than about two children in a
thousand of this regular school population would be expected to be 3 or
more years retarded and thus overlap those of like deficiency in the
special classes (_167_, p. 30). Considering the results of Norsworthy's
study he says on similar assumptions: “It seems, therefore, that a
carefully planned psychological test, while not sufficing to
differentiate 50 to 60% of the mentally defective from the normal child,
would suffice to differentiate 40 to 50%” (_164_, p. 35). Again we come
back to the estimate that psychological tests may well be expected to
select nearly half of the children at present found in special classes
for retarded pupils. Moreover, a considerable part of the overlapping of
intellectual deficiency in the regular classes with that in the special
classes which he found may be accounted for by the inadequate methods of
selection of pupils for the special classes by teachers or examiners who
have used no objective tests. Some who were left in the regular classes
should undoubtedly have been transferred to special classes and vice
versa. There seems to be nothing to indicate that less than half of
those properly sent to special classes would be of clear or doubtful
intellectual deficiency. If the tests served to select even a smaller
proportion of those assigned to special instruction, the “school
inefficients” as Pearson calls them, their value as an aid to diagnosis
would be demonstrated.
Among groups of delinquents, where we would expect the purely conative
cases to be more common, we find that a careful diagnosis of
feeble-mindedness on the basis of test data, medical examination and
case history indicates that conative cases without serious intellectual
deficiency are much rarer than intellectually deficient delinquents. At
least this is the evidence of one study where such information is
available. Kohs at the Chicago House of Correction found among 219 cases
over 16 years of age, which he diagnosed as feeble-minded, only 28
tested XI and there were only 52 who did not test either presumably
deficient or uncertain intellectually according to our criterion.
Another bit of evidence is that collected at the Clearing House for
Mental Defectives in connection with the New York Post-Graduate School
of Medicine, where 200 consecutive cases (108 males) were examined by
Miss Hinckley. Her graphs show that only 15% tested X or above with the
Binet revised scale, _i. e._, above those presumably deficient in
intellect. The cases were from 13 to 42 years of age. The clearing house
provides an opportunity for social workers to have suspected deficients
examined and the few cases over X seems to indicate that the purely
conative type is not very commonly met with among the social workers.
When we turn to the institutions for the feeble-minded we find that they
are today caring for few solely conative cases. Although I can find no
tables which give both the life ages and mental ages of the individual
inmates, we can at least be sure that few test so high as X, or above
with the Binet scale. This means that only a few have as yet reached the
threshold for passable adult intellects, which should be attained by 15
years of age. At the Minnesota state institution for the feeble-minded
in Faribault among 1266 inmates, excluding epileptics, 41 tested X; 28,
XI; 12, XII; and 8, XIII, a total of 7% (_154_). At Vineland, N. J.,
Goddard reported among 382 inmates, 14 tested X; 5, XI; and 7, XII,
about 7%. Some of the children who were under 15 in life-age might later
develop above the limit for intellectual deficiency. Of the 1266 at the
Minnesota institution, however, 508 were 15 or over at the time of their
admission, so that at least 82% of the 508 were clearly intellectually
deficient. Eight per cent. more tested X and were in the doubtful group
in intellectual ability according to the criteria we have adopted. This
suggests that not more than about 10% of those who are at present
isolated in institutions are there for feebleness of will alone. It
seems to confirm our presumption that the intellectually deficient
discovered by tests form the great majority of the social deficients who
need prolonged care or assistance.
(d) ALLOWANCE MAY BE MADE FOR VARIABILITY.
The quantitative definition of intellectual deficiency must be made with
careful allowance for irregularities among different mental processes,
among different individuals, and among different groups. Theoretically
it is possible to place the borderline so low that a case with that
degree of deficiency and without removable handicaps would be clearly
feeble-minded. The chance that the diagnosis would be mistaken could be
reduced to any minimum desired. Above this a wider region of doubtful
deficiency could then be stated in similar form. This is the plan that
we suggest in attempting the percentage definition. Practically,
however, the plan assumes that a suitable allowance can actually be made
for these variations and raises a number of problems as to variability
which should be considered. Four of these sources of variation are
discussed below: (1) the variation due to a limited sample of
individuals measured, (2) the variation among different communities, (3)
the variations arising from sex, race and social differences, (4) the
variation of the same individual from one mental process to another. We
do not have the problem of neglecting these variations, but of
adequately allowing for them both in the percentage of presumably
deficient and in the doubtful region.
(1) _Variation among Samples of Individuals Measured._ The error
introduced by the fact that measurements are made on a limited rather
than an unlimited number of individuals, in establishing the standards
with a system of tests, can be taken care of statistically fairly well
by applying the theory of probability as to the error of a percentage in
a single sample. The range of the error can then be indicated on the
measurement scale. This supposes, however, that each sample to be
measured is taken from a random group and not from a selected group.
Allowance for this error of sampling is therefore complicated by the
fact that the usual test data have been obtained from groups of _school
children_, even when there has been no further selection within the
school group. Data on school children are certainly reliable only within
the years of compulsory school attendance. Ordinarily in this country,
they are not reliable for children of 14 years of age or over. Moreover,
the point of the scale which is reached by the lowest X percentage of
school pupils will exclude a slightly larger percentage of all children
of corresponding ages, since the idiots and some imbeciles are not sent
to the ordinary schools. This slight discrepancy should be kept in mind.
The problem of avoiding selected samples among adults is still more
difficult; but we found that it was possible in one community at least
to measure all the 15-year-olds in the lowest X percentage in certain
districts, as we shall note later. By this age, mental processes are
probably very much like those of adults, except for the amount of
information and practise.
(2) _Variation among Different Communities._ Under any conception of
deficiency it is clear that there are relatively more deficients in some
communities than others. The percentage should, of course, not be
determined for a small community such as a city or county, but for a
state or a nation in order to avoid the difficulty of the difference
between communities. It would not interfere with the plan for isolating
the lowest X percentage of a state even if that meant isolating 10% in
one small community and none in another. Indeed, it might be expected to
do just that, when one considers the accumulation of deficiency in
certain settlements such as Key has shown (_131_, p. 63). The data on
which the borderline with a measuring scale would be established should,
of course, not be obtained from communities known to be unusual in
respect to the frequency of deficiency.
Since social failure is our final criterion for judging deficiency, we
must further consider that it is easier for a person to survive in one
environment than in another: in the country, for example, than in the
city. This sort of problem has led to considerable confusion. Goddard
remarks: “In consequence of this it happens that a man may be
intelligent in one environment and unintelligent in another. It is this
point which Binet has illustrated by saying 'A French peasant may be
normal in a rural community but feeble-minded in Paris.'” (_117_, p.
573.) Goddard then goes on to suppose that a delinquent with the
intelligence of a sixteen year old may be “defective” because he happens
“to have got into an environment that requires a twenty-year-old
intelligence.” The suggestion that a criminal might be excused on the
ground of deficiency because he happened to fall among bad companions is
a _reductio ad absurdum_. Clearly environment must be defined as
ordinary environment, available environment or by some similar concept,
or else the definition of deficiency loses all significance. In another
place Goddard more properly suggests that it would be well to “draw one
line at that point below which a person of that intelligence is not
desirable or useful _in any environment_” (_117_, p. 3).
So long as the care of the feeble-minded is a state problem the
percentage of passable intellects would apparently be determined for the
available environment in that state. The problem of social care cannot
mean that the state should care for college men because they cannot
survive among college men or in the station of life into which they may
have been born. So long as there are environments within the community
where they can survive it is a problem of shifting them in their social
habitat, not a problem for social care. The same is true for the low
grades of intellect. It is not likely, however, that any portion of the
community could absorb many more of the low degree intellects. For the
problem of social care for the feeble-minded, the question: What
environment will allow this individual to survive? becomes the question:
Can he survive in any available environment in his community? It would
seem very hazardous to suppose that the different opportunities for
survival afforded by different localities in a state would be large
enough to care for more than the group of doubtful cases which should be
allowed for in a quantitative description of the border region.
(3) _The Variation with Sex, Race, and Social Position_ has been
carefully called to attention by Yerkes and Bridges in their studies
with the Binet Point Scale (_225_, Chap. V and VI). It may very well be
that not as high ability should be expected of certain groups as of
others; as a matter of moral obligation, they are not as responsible for
their conduct or their attainments. On the other hand this does not
directly affect the question, what lowest percentage of intellects
cannot get along in society? When that percentage is determined for the
environment available in the community all those who fall within it
might even turn out to be of one sex or of one nationality or of one
social position, without affecting the question whether they should be
cared for by society, or what grade of intellect is not socially
passable? Temporary social handicaps, such as lack of familiarity with
the language, lack of training, etc., must, of course, be allowed for so
far as they affect the individual's test record. Whether the difference
of 5% to 10% in the score of pupils born to non-English-speaking
families compared to their companions' (_225_, p. 66) is due to the
temporary handicap of language or to a permanent difference is, however,
just the problem which the Yerkes and Bridges study does not answer. The
fact that the difference is even greater for older children suggests
that it may indicate an inborn difference between the groups compared.
A diagnosis of deficiency should not be made until the examiner is able
to estimate whether the removal of training or health handicaps would
bring the individual above the borderline. So far as known temporary
handicaps affect the standard of the test results with groups they
should, of course, also be taken into account. On the other hand, it is
clear that the borderline which predicts social failure should not be
shifted to allow for differences in permanent handicaps whether those be
of race, sex or social position.
(4) _The Variation among Different Mental Processes._ With our present
knowledge the most difficult variation for which we must make allowance
at the borderline is the variation from one trait or process to another
in the same individual. One phase of it was discussed above under “c.”
The investigation of Norsworthy throws light on this question.
Summarizing her tests she says: “Among idiots there is not an equal lack
of mental capacity in all directions. There is something of the same
lack of correlation among the traits measured in the case of idiots as
there is with ordinary people” (_159_, p. 68). Again: “The idiots are
nearest the central tendency for children in general in the measurements
of mental traits which are chiefly tests of maturity, and farther and
farther away as measurements are made which are tests of ability to deal
with abstract data. They are two and a half times as far from the median
for children in general in tests like the genus-species test as they are
in tests like the A test or the perception of weight.” Weidensall (_60_)
and Pyle (_46_) also compare delinquent and normal individuals for
different tests, showing a variation with the sort of mental activity
compared.
While Norsworthy thus presents evidence of certain specializations of
deficiency, she notes, however, that perhaps feeble-mindedness is more
typically general than specific and that general deficiency is more
important to consider than specific. Even with that test with which her
group of retarded and feeble-minded children did best, only 28% of them
passed the point which would be excelled by 75% of the children in
general. In their worst test only 1% passed this point. It is also to be
noticed that those tests in which they most nearly approached ordinary
children are for just those simple processes which would be least likely
to be of use in the struggle for social existence. As a whole,
therefore, there is nothing in her results which shows that any
appreciable number of children who were deficient in the average of
tested abilities, would have good enough special ability along a few
lines to make them socially passable. Indeed, for all that we know at
present, the borderline for _passable ability_ in each of our various
mental processes might vary quite as much as Norsworthy found, without
this variation affecting a prediction of failure based upon the average
of a series of tests.
On account of the great attention that has been paid to individual
differences in recent years, on account of their importance for
diagnosis, for determining the causes of deficiency, and for planning
for the training of deficients, we have come almost to the point where
we forget the significance of the average as the most common condition
with which we have to deal. The lack of complete correlation between
abilities of an individual does not make us hesitate to use the concept
of his average ability; it should not make us neglect or misunderstand
the significance of the position of an individual testing low down on
the scale. For the problem of social care the borderline position on a
scale is immensely more important than higher ability. It seems
advisable, therefore, to define this borderline ability with some
suitable allowance for variability in mental processes. It is far safer
to judge an individual's chance of survival by his average or general
tested ability than by the little knowledge that is as yet available
regarding special abilities.
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Footnote 4:
AUGUSTA F. BRONNER. _The Psychology of Special Abilities and
Disabilities._ Boston, 1917, pp. vii, 269.