Statistical Study
The statistical study compared two groups of cases in respect to I.Q. These groups were selected from one large group, on the basis of presence or absence of tonsillar defect. The tonsil group was composed of 236 cases, and the normal group, of 294. The distribution of the two groups according to intelligence is set forth in Table I, and in Figs. I and II.
TABLE I
| Tonsil Group | Normal Group | |||
| I.Q. | No. of Cases | Per cent of Cases | No. of Cases | Per cent of Cases |
| 40- 50 | 2 | ·8 | 0 | 0 |
| 50- 60 | 1 | ·4 | 2 | ·7 |
| 60- 70 | 7 | 2·9 | 4 | 1·4 |
| 70- 80 | 21 | 8·9 | 29 | 9·8 |
| 80- 90 | 45 | 19·0 | 52 | 17·7 |
| 90-100 | 80 | 33·9 | 107 | 36·4 |
| 100-110 | 55 | 23·3 | 67 | 22·8 |
| 110-120 | 17 | 7·2 | 24 | 8·1 |
| 120-130 | 6 | 2·5 | 9 | 3·0 |
| 130-140 | 2 | ·8 | 0 | 0 |
| 140-150 | 1 | ·4 | 0 | 0 |
| Average | 94·9 | 95·4 | ||
| Median | 95·3 | 95·6 | ||
| Q | 8·705 | 8·27 | ||
| σ | 14·4 | 12·2 | ||
From these it is evident that the two groups are practically equal in intelligence. The average I.Q. for the normal group is 95·4, as compared with 94·9 for the tonsil group. The medians are equally close,—95·6 in the normal group and 95·3 with the tonsil cases. The difference in variability is negligible, Q being 8·705 and σ 14·4 in the tonsil group, while in the normal Q is 8·27 and σ 12·2. The two cases with the lowest I.Q.'s were tonsil cases, but the three highest I.Q.'s also belong in this group.
Fig. 1. Distribution of I.Q.'s. Number of cases.
Fig. 2. Distribution of I.Q.'s by percentage of total number of cases in the group.
If the frequencies are expressed in terms of per cent of the total number of cases in the group, the two may be compared further. The following details are noticeable.