| Causes | 151 children 1-9 to 3-9 | 19 children 3-9 to 6-9 |
| Irregular attendance | 51 | 6 |
| Adenoids | 24 | 2 |
| Inherent dullness | 59 | 11 |
The term "cause" seems to be rather loosely used in this study. The author says concerning this,
"Dealing with physical defects first, although they amount in the aggregate to 53 per cent (omitting defective speech, which is a secondary condition), in 10 percent only do they represent the whole cause. This is made up of those cases where the defect is of such intensity as to produce retardation in otherwise ordinary children, and of other cases of less intensity, but sufficient to weigh down the balance against those near the level of what we may call for convenience the lower limit of normal intelligence." How he determines, without removing a defect, what the child's intelligence would be without it he does not explain.
The following table compares the physical condition of two groups, one comprised of children examined in the regular routine examinations during the year 1912,—the other a group of retarded school children, given a special examination:—[10]
| Group I | Group II | |
| No. of children examined | 287,456 | 1,541 |
| No. with physical defects | 206,720—71·9% | 1,383—89·8% |
| No. of defects found | 226,639 | 2,986 |
| Defect | No. | % | No. | % | |||
| Anaemia | 335 | 23·0 | |||||
| Malnutrition | 8,303 | 2·9 | 557 | 36·1 | |||
| Defective vision | 21,078 | 9·3 | 536 | 34·7 | |||
| Defective hearing | 1,206 | 0·5 | 47 | 3·0 | |||
| Defective nasal breathing | 21,931 | 7·6 | 316 | 20·4 | |||
| Hypertrophied tonsils | 30,021 | 10·4 | 297 | 19·2 | |||
| Defective teeth | 142,168 | 49·4 | 796 | 51·6 | |||
| Pulmonary disease | 335 | 0·1 | 47 | 3·0 | |||
| Cardiac disease | 1,597 | 0·5 | 35 | 2·3 | |||
| Average No. of defects per child | 1·1 | 2·5 | |||||
In an investigation of 3,587 exempt and 1,418 non-exempt children in the Philadelphia schools,[11] Dr. Newmayer found the following percentages of defect:
| Exempt Children | Non-exempt Children | |||
| Defect | No. Examined | % | No. Examined | % |
| Defective vision | 371 | 10·0 | 171 | 12·0 |
| Defective hearing | 49 | 1·4 | 29 | 2·0 |
| Defects of nose | 54 | 1·5 | 21 | 1·5 |
| Defects of throat | 137 | 3·8 | 53 | 3·7 |
| Orthopedic defects | 25 | ·7 | 25 | 1·8 |
| Mentally defective | 6 | ·1 | 80 | 5·6 |
| Skin diseases | 918 | 26·0 | 423 | 30·0 |
| Miscellaneous | 214 | 6·0 | 128 | 9·0 |
| Total | 1,774 | 49·0 | 930 | 65·0 |
It is evident from the majority of these investigations that there is some relationship between physical defects and pedagogical retardation. But whether or not the relationship is a causal one, they do not indicate. Simple co-existence of two characteristics is not necessarily significant that one is cause of the other. Plainly, though, if the removal of a physical defect is followed by improvement in the school progress, it may be argued that the presence of the defect was a causal factor in the previous retardation. The method in the few following studies, which seems to be employed to a greater degree than formerly, consists of measurement of such improvement.
The Journal of Psycho-Asthenics, March and June, 1918, contains a paper on the "Results obtained from the Removal of Tonsils and Adenoids in the Feeble-minded," by Wm. J. G. Dawson, M. D. The author starts out rather discouragingly by regarding his hypothesis as an axiom. He says,