A first study of the inheritance of vision and of the relative influence of heredity and environment on sight / by Amy Barrington and Karl Pearson.

  • Barrington, Amy.
Date:
1909
Catalogue details

Licence: In copyright

Credit: A first study of the inheritance of vision and of the relative influence of heredity and environment on sight / by Amy Barrington and Karl Pearson. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

    14/74 (page 8)
    school children were examined, and the boys (16,233) showed in S'd/^ of cases, the girls (16,421) in 10'6 7o of cases an astigmatism which alone or to a great part affected their keenness of vision. Now if the selection were simply made on the basis of excessive astigmatism according to the rule we should find the mean increased but the standard deviation decreased after the ophthalmologist had made his selection. But this is very far from the fact. In all cases of material selected as possessing defective vision the mean of the corneal astigmatism is raised, but at the same time the standard deviation is very largely raised also. This follows because the classes of astigmatism against the rule, i.e. the persons with the greater curvature in the horizontal meridian, noted in the above table with a minus sign, are also largely selected. Excess of astigmatism according to the rule is more frequent than excess against the rule ; the curve of distribution in the general child is not very widely different from normality, but the tail according to the rule is sensibly exaggerated beyond the tail against the rule, i.e. there is skew- ness in the sense of the positive astigmatism. The selection curve is actually U-shaped and the resulting standard deviation much increased. Unfortunately we have not the numbers but only Steiger's diagram of the percentages of each class in the selected children ((B) xvi. p. 237), but it is sufficient to indicate that if these could be reduced to percentages of each class in the normal Berne population we should find a skew U-curve for our selection curve. The following is our rough attempt to reach this from Steiger's diagram taking Boys ((a) above) as the normal population. Ophthalmological selection from general boy population of 8*5 of astigmatics: ' Against the Eule' 0 0-25 0-5 0-75 1 1-25 1-75 2-625 Over 3 Distribution of 8'5°/ Percentage of each class of normal population taken •17 212 •24 4^1 •33 2^9 •57 1-8 •46 \-7 •46 4-2 •66 8^9 2-27 78-3 1^76 103-5 1-58 175^6 This brings out the skew U-shaped nature of the selection curve. The two last percentages exceeding 100 7o show that all the individuals at Zurich with 2*0 D or more were actually selected and that in the Berne population there were fewer of these cases than existed in Zurich. The mean of the selected Zurich boy population is 1*89 D and the standard deviation 108 D*; thus indicating that the mean has been more than doubled, and the standard deviation not quite doubled. Of course this rough result cannot be directly applied from children to adults, but it may suffice to indicate the direction of ophthalmological selection. It is not a simple selection which cuts off one tail only of the distribution. Another point is also to be noticed. In actual practice the selection will most generally be of adults, and the corneal astigmatism of these will be different from that of children. Steiger's results ((A) p. 22) are very regular, and show sensible decrease of * Based on the values of the 8 5 distribution given above.