It is, of course, very desirable that the results obtained by Goddard as well as our Minneapolis results should be checked by data on unselected groups elsewhere. With the 1908 scale the only other data which seems fairly to represent a random selection are those of Terman and Child's (195, p. 69). Since they examined less than 50 at any age, however, their table helps only to check roughly the borderline suggested. The percentages retarded two years or more changed to the basis of calculation we used, indicate that the break comes at 10 years. The percentages from six up to ten years run 0, 3, 7, 6, when they change to 12% or more for the following ages. While the groups are too small to indicate the borderlines for each age, yet, when we group the children from 6-9 years inclusive, under our interpretation we find that a year less than our upper borderline for the uncertain group would give 4.8% of 147 cases. With 142 cases in the group 10, 11, and 12 years old, 5.6% would be caught by placing the borderline for the doubtful a year less than we have indicated. Our scale borderlines are thus in harmony with these data.
(b) Data For Other Developmental Scales.
When we turn to data from randomly selected groups for judging the borderlines with other developmental scales than the 1908 Binet, we find that a group of children in the rural schools of Porter County, Indiana, have been examined with the Goddard adaptation of the Binet 1911 scale ([92]) and a group of school children in a Minnesota city, with the Kuhlmann adaptation of the 1911 scale ([138]). The important results with each study are given in Table VI. In the Indiana study the children were examined through the eighth grade. The elimination of older children from school would certainly affect the groups over 13 years of age and probably disturb the results even for the 13-year olds. For this group the results are published only for nearest mental and nearest life-ages. The results are, therefore, not strictly comparable with those of Table V. for the 1908 scale. It is doubtful whether tests on children in the rural schools should be used for indicating borderlines. The table suggests, however, that the borderlines we have indicated for the 1908 scale are not too conservative for the immature tested with the 1911 scale. It is possible, however, that with Goddard's adaptation the break comes at 9 years of age instead of 10.
TABLE VI.
TABLE VI.—Mental Retardation of Children as Tested with the 1911 Binet Scale
Children in the Rural Schools of Porter County, Indiana, tested with the Goddard 1911 scale. (From Table XIII, U. S. Public Health Bulletin, No. 77)
| Nearest Life-Ages | Total Pupils | Percentages showing the following years of tested retardation according to the nearest mental ages: | |||
|---|---|---|---|---|---|
| Two or more | Three or more | Four or more | Five or more | ||
| 6 | 107 | 2.8 | |||
| 7 | 232 | 6.03 | .43 | ||
| 8 | 234 | 8.12 | 2.12 | .42 | |
| 9 | 216 | 12.04 | 5.54 | 1.84 | .92 |
| 10 | 278 | 19.88 | 3.58 | 1.08 | .36 |
| 11 | 212 | 18.3 | 8.4 | 1.8 | |
| 12 | 243 | 33.9 | 12.9 | 2.6 | |
| 13 | 249 | 63.7 | 27.9 | 8.4 | 2.8 |
Number of Pupils Testing retarded according to Kuhlmann's revision of the Binet 1911 scale. (From Kuhlmann's Table VIII.)
| Exact years of retardation. | ||||
|---|---|---|---|---|
| Nearest Life-Age | Total Pupils | 1 or more | 2 or more | 3 or more |
| 6 | 38 | 0 | 0 | 0 |
| 7 | 82 | 4 | 0 | 0 |
| 8 | 95 | 9 | 0 | 0 |
| 9 | 91 | 12 | 2 | 0 |
| 10 | 84 | 16 | 9 | 1 |
| 11 | 88 | 18 | 4 | 0 |
| 12 | 75 | 32 | 8 | 1 |
Kuhlmann, with the assistance of twenty teachers whom he started in the work and whom he regards as “untrained examiners,” measured “the public school children from the first to the seventh grade, inclusive, in a Minnesota city.” The essential figures from his results are given in Table VI. These results are not directly comparable with those of Goddard using the 1908 scale, since Kuhlmann tabulates the nearest ages instead of the actual ages. His age groups would therefore average a half year younger chronologically than Goddard's. Moreover, the exact amount of retardation to tenths of a year was then calculated from the exact age, and it is to be remembered that the method of calculating the mental age was changed in 1911 so as to start with a basal age in which all tests were passed. The effect of these changes would be that some of those recorded in Kuhlmann's table as two years retarded might easily be a year more retarded under the same methods of calculation that were previously used. Using his method of computation, it is clear that the general borderline for the immature with this scale would not be as low as we have indicated for the 1908 Binet scale. It would apparently be about a year less, i. e., two years of retardation for those six to nine years of age, and three years retardation for those 10 or above in order to fall within our doubtful group. The 13 year old group are not included here. They would not be even approximately random since those who had reached the eighth grade or above were not examined. It is interesting to note that the break in frequency of serious retardation again occurs in the change from those chronologically 9 years of age to those 10 years of age.