CHAPTER II. THE FUNCTIONS OF A SCALE IN DIAGNOSIS

A. The Meaning of Intellectual Deficiency.

Whatever form the definition of feeble-mindedness may take, in this country at least^[3] the concept has become quite firmly established as describing the condition of those who require social guardianship, because, with training, they do not develop enough mentally to live an independent life in society. The feeble-minded are socially deficient because of a failure to develop mentally. They are proper wards of the state because of this mental deficiency. Goddard says, they are “incapable of functioning properly in our highly organized society” (112, p. 6). The most generally quoted verbal description of the upper line of social unfitness is that of the British Royal Commission on Feeble-Mindedness: “Persons who may be capable of earning a living under favorable circumstances, but are incapable from mental defect existing from birth or from an early age (a) of competing on equal terms with their normal fellows; or (b) of managing themselves and their affairs with ordinary prudence.” It is clear that the intention is to distinguish mental deficiency from senile dementia, from hysteria and from insanity, in which there is a temporary or permanent loss of mental ability rather than a failure to develop. Feeble-mindedness may, however, arise from epilepsy or from other diseases or accidents in early life as well as from an inherent incapacity for development. Moreover, mental deficiency, or feeble-mindedness, (I use the terms interchangeably) does not imply that the social unfitness is always caused by intellectual deficiency. Mind is a broader term than intellect, as we shall note in the next section.

This definition of the feeble-minded is the main idea expressed by Witmer (221), Tredgold (204), Pearson (164), and Murdock (164). The historical development of the concept is traced by Rogers (172) and Norsworthy (159). It is criticized by Kuhlmann (140) as impractical and indefinite. The indefiniteness is indicated by such terms as “under favorable circumstances,” “on equal terms,” and “with ordinary prudence.” This objectionable uncertainty as to social fitness can be considerably relieved for those types of feeble-mindedness which involve the inability to pass mental tests, since this result can later be correlated with subsequent social failure and predictions made during childhood on the basis of the tests. Attempts to make the concept of feeble-mindedness more definite have, therefore, naturally taken some quantitative form in relation to objective tests. Binet and the French commission in 1907 (77) called attention to the method in use in Belgium for predicting unfitness objectively on the basis of the amount of retardation in school at different ages. With the appearance in 1908 of the Binet-Simon revised scale for measuring mental development, quantitative descriptions began to be concerned with the borderlines of mental deficiency on scales of tests.

While the quantitative descriptions of tested deficiency do not include all forms of feeble-mindedness, as I shall show in the next section, they have made the diagnosis of the majority of cases much more definite. Nobody would think of returning to the days when the principal objective criteria were signs of Cretinism, Mongolianism, hydrocephalus, microcephalus, epilepsy, meningitis, etc., which LaPage (141) has shown are not found among more than 9% of 784 children in the Manchester special schools. The impossibility of agreeing upon subjective estimates of mental capacity without the use of objective criteria is well shown by Binet's methodical comparison of the admission certificates filled out within a few days of each other by the alienists for the institutions of Sainte-Anne, Bicêtre, the Salpêtreire and Vaucluse. These physicians gave their judgments as to whether a case was an idiot, imbecile or higher grade. Binet says: “We have compared several hundreds of these certificates, and we think we may say without exaggeration that they looked as if they had been drawn by chance out of a sack” (77, p. 76).

The rapid accumulation of data with psychological tests has made it possible to take our first halting steps in the direction of greater definiteness in diagnosis by a larger use of objective methods. This increase in significance of the concept of deficiency is fruitful at once in estimating the size of the social problem and planning means for undertaking the care of these unfortunates. We can discover something of the error in the previous subjective estimates of the frequency of feeble-mindedness. We can bring together and compare the work of different investigators, not only in our country, but throughout the world. We can discover, for example, how important the problem of deficiency is among different groups of delinquents, knowing that the differences are not to be explained by differences in expert opinion. Furthermore, we can now determine, with considerable accuracy, whether the diagnosis made by a reliable examiner is independent of his personal opinion.

If we disregard the natural antipathy of many people to anything which tends to limit the charming vagueness of their mental outlook, we may endeavor to chart this horizon of tested deficiency with something of the definiteness of figures, which shall at the same time indicate a range of error. As soon as our aim comes to be to plot the borderline on a measuring scale of mental ability, we find that the borderline must be so stated that we can deal with either adults or children. Two sorts of limiting regions must be described, one for mature minds and one for immature minds. The latter will be in the nature of a prediction as to what sort of ability the children will show when they grow up. We must keep in mind, therefore, that we should attempt our quantitative definition for both growing and adult minds. As soon as the growing mind passes the lower limit for the mature it is then guaranteed access to the social seas although it may never swim far from shore nor develop further with advancing years. In seeking greater definiteness, our aim should then be to describe both the limit for the mature individuals and the limit for the immature of each age. In this paper the definition will be restricted to intellectual deficiency, i. e., tested deficiency. It will take the form of describing the positions on a scale below which fall the same lowest percentage of intellects. This percentage definition of intellectual deficiency offers such a simple method of consistently describing the borderlines for mature and immature that it is surprising so little attempt has previously been made to work it out for a system of tests. Although the principle on which the definition is based depends upon the distribution curve of ability, it is concerned only with the lower limit of the distribution. Since the exact form of this distribution is uncertain I have preferred to call it a percentage definition of intellectual deficiency rather than to state the limits in terms of the variability of ability. Moreover the lowest X per cent. in mental development requires no further explanation to be understood by the layman.

B. Forms of Mental Deficiency Not Yet Discoverable by Tests.

The first broad conclusion that impresses those who try to use mental scales for diagnosing feeble-mindedness is that the lower types, the idiots and imbeciles, can be detected with great accuracy by an hour's testing. The difficulties pile up as soon as the individual rises above the imbecile group. The practical experience of those in institutions for the feeble-minded here becomes of fundamental importance. They are able to supply the history of exceptions that should make us cautious about our general rules. Certain people whom they have known for years to be unable to adjust themselves socially because their minds have not reached the level of social fitness will yet be able to pass considerably beyond the lower test limit for mature minds. The mental scales can only detect those feeble-minded who cannot succeed with our present tests. This is the basal principle in using any system of tests.

Stated in another way, this first caution for anybody seeking the assistance of a mental scale is that tests may detect a feeble-minded person, but when a person passes them it does not guarantee social fitness. The negative conclusion, “this person is not feeble-minded,” can not be drawn from tests alone. Mental tests at present are positive and not negative scales. This fact will probably always make the expert's judgment essential before the discharge of a suspected case of mental deficiency. When a subject falls below a conservative limit for tested ability a trained psychologist who is familiar with the sources of error in giving tests, even without experience with the feeble-minded, should be able to say that this person at present shows as deficient development as the feeble-minded. To conclude however that any subject has a passable mind requires in addition practical experience with feeble-minded people who pass the tests. It is very much easier to state that the tests do not detect all forms of feeble-mindedness than it is to give any adequate description of the sort of feeble-mindedness which they do not as yet detect.

This distinction between the feeble-minded who do well with test scales and those who do not, is well known in the institutions for the feeble-minded. Binet sought to distinguish some of the feeble-minded who escaped the tests by calling them “unstable,” or “ill-balanced,” individuals as Drummond (77) translates the term. To use the historical distinctions of psychology, their minds seem to be undeveloped more on their volitional and emotional sides than on their intellectual side. Weidensall (59) has described another type as “inert.” She found that quite a number of the reformatory women might slide through the tests but fail socially from the fact that “their lives and minds are so constituted that they feel no need to learn the things any child ought to know, though they can and do learn when we teach them.” Again, it seems to be a disturbance of will through the feeling, rather than an intellectual deficiency. Many of the so-called “moral imbeciles” are probably able to pass intellectual tests lasting but a few minutes. Like the unstable or inert they are not failures because of a lack of intellectual understanding of right and wrong, but because of excess or deficiency of their instinctive tendencies especially in the emotional sphere. Such weakness of will may arise either from abnormality of specific instinctive impulses or inability to organize these impulses so that one impulse may be utilized to supplement or inhibit another. We may call all this group of cases socially deficient because of a weakness in the volitional, or conative, aspect of mind.

The discrimination of mental activities which are predominately emotional and conative from those in which intellect is mainly emphasized is also well recognized by those who have been making broad studies of tests in other fields than that of feeble-mindedness. Hart and Spearman (123), for example, call attention to the fact that tests passed under the stimulus of test conditions represent what the subject does when keyed up to it rather than what he would do under social conditions. We cannot be sure that speed ability as tested will represent speed preferences. The subject may be able to work rapidly for a few minutes, but in life consistently prefer to work deliberately. Regarding the eighteen tests which they studied with normal and abnormal adults they say: “These tests have been arranged so as to be confined to purely intellectual factors. But in ordinary life, this simplicity is of rare occurrence. For the most part, what we think and believe is dominated by what we feel and want.” Kelley (130) finds by the regression equation that the factor of effort amounts to two-thirds of the weight of that of the intellectual factor in predicting scholarship from teachers' estimates. Webb (217) thinks that he finds by tests a general conative factor comparable to Spearman's general intellective factor.

With the change in point of view that has come from the adoption of the biological conception of the mind the discrimination of the different forms of feeble-mindedness must be recognized as a distinction in the emphasis on intellectual, emotional and conative processes, not a distinction between actually separable forms of mental activity. On account of the organic nature of the mind it is well established that various mental processes are mutually dependent. Any disturbance of the emotional processes will tend to affect the thinking and vice versa. Even if we believe that emotions are complex facts, involving vague sensations as well as feelings, and that terms like emotion, memory, reasoning and will are names for classes of mental facts rather than for mental powers, it still remains important to distinguish between feeling, intellect and will, as well as to recognize the interdependence of the mental processes. Common sense seems to agree with psychological descriptions in regarding mind as a broader term than intellect, and feeble-mindedness as a broader term than intellectual feebleness.

Since tests at present tend to reach the intellectual processes more surely than the emotional, we describe those who fail in them as intellectually deficient. The term “intellect” seems to be better than “intelligence” because the latter seems to include information as well as capacity, while the aim of measuring scales has been to eliminate the influence of increasing information with age. To be thoroughly objective, of course, one should talk about “feebleness in tested abilities;” but we would then fail to point out the important fact about our present scales that they detect mainly intellectual deficiency, that they do not reach those forms of feeble-mindedness in which the weakness in such traits as stability, ambition, perseverance, self-control, etc., is not great enough to interfere with the brief intellectual processes necessary for passing tests. Intellectual deficiency will be used hereafter to refer to those social deficients whose feebleness is disclosed by our present test scales.

In the opinion of Kuhlmann these cases of disturbed emotions and will which shade off into different forms of insanity should not be classed as feeble-minded at all, although he recognizes that they are commonly placed in this group. He regards them as an intermediate class between the feeble-minded and the insane. He says: “They readily fail in the social test for feeble-mindedness and because of the absence of definite symptoms of insanity are often classed as feeble-minded. In the opinion of the present writer they should not be so classed, because they require a different kind of care and treatment, and have a different kind of capacity for usefulness” (140). So long as this group of what we shall term “conative cases” is discriminated from the intellectually deficient it matters less whether they be regarded as a sub-group of the feeble-minded or as a co-ordinate class. In grouping them with the feeble-minded we have followed the customary classification. An estimate of the size of this group will be considered later in Chapter III.

C. Doubtful Intellects Accompanied by Delinquency Presumed Deficient.

Conative forms of feeble-mindedness are perhaps the most serious types in the field of delinquency. They are the troublesome portion of the borderland group of deficient delinquents about which there is so much concern. It is important to remember that it is just among these cases that the test judgment is least certain. In this dilemma one principle seems to be sound enough psychologically to be likely to meet with acceptance. I should state this principle as follows: A borderline case which has also shown serious and repeated delinquency should be classed as feeble-minded, the combination of doubtful intellect and repeated delinquency making him socially unfit. This will relieve the practical situation temporarily until tests are perfected which will detect those whose feebleness is specialized in those phases of volition centering around the instinctive passions, control, balance, interest and endurance. The principle recognizes that mental weakness is sometimes emphasized in the volitional processes of the mind.

The principle is apparently in conflict with the rule advocated by Dr. Wallin. Referring to the mental levels reached by individuals, he says: “We cannot consider X-, XI-, or XII-year-old criminals as feeble-minded because they happen to be criminals and refuse to consider X-, XI-, and XII-year-old housewives, farmers, laborers and merchants as feeble-minded simply because they are law abiding and successful” (214, p. 707). At another place he insists “that the rule must work both ways” (215, p. 74). Logically it would seem at first that it was a poor rule which did not work both ways. Further consideration will show, I believe, that there has been a confusion of feeble-mindedness with tested deficiency. If all the feeble-minded tested deficient intellectually then the tested level should determine whether or not they were feeble-minded. This, however, is not a correct psychological description of the facts. I prefer, therefore, to allow for those in a defined narrow range of weak intellects to be classed as deficient provided their weakness also manifests itself pronouncedly in the conative sphere.

The principle that all mental deficients need not show the same low degree of intellectual ability is clearly recognized in perhaps the most important legal enactment on deficiency which has been passed in recent years, the British Mental Deficiency Act of 1913. It states regarding “moral imbeciles” that they are persons “who from an early age display some permanent mental defect coupled with strong vicious or criminal propensities on which punishment has had little or no deterrent effect.” It specifically distinguishes them from the group of feeble-minded which require guardianship because of inability to care for themselves.

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.