The application of the mean values derived from a large number of measurements to the annual physical examinations of cadets of the Naval Academy / by Henry G. Beyer.

  • Beyer, Henry Gustav, 1850-1918.
Date:
[between 1890 and 1899]
Catalogue details

Licence: Public Domain Mark

Credit: The application of the mean values derived from a large number of measurements to the annual physical examinations of cadets of the Naval Academy / by Henry G. Beyer. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    5/6 (page 109)
    individual measured. The absolute annual increase is commonly greater in a big boy than in a small boy, and yet the rate of growth may be the same. The relative annual increase is free of such errors (Porter). (6) With the assistance of tables such as the preceding it is, comparatively speak- ing, a simple matter to ascertain the relative position of any individual measured to the mean of his age, and the question so often asked, is this young man above or below the mean of his age in weight, height, circumference of chest, lung capacity, may be easily answered by a reference to the values presented in Table III. It is, however, not so simple as would appear to determine the probable degree of abnormality of any observed deviation from the mean. For the solution of this problem Prof. W. T. Porter has proposed the following method: According to the theory of probabilities, the heights of a thousand individuals of the same class will arrange themselves as follows: Between. Individuals. M + 4d and M + nd 3 M + 3d and M -j- Id 18 il + 2d and M + 3d 67 il- + d and 31 + 2d 162 M and M + d 250 il and M d 250 it d and M - 2d 102 M 2d and AI — 3d 67 M — 3d and M — 4d 18 il 4d and M — nd 3 Where M = the mean and d = the probable deviation. Prof. Porter now proceeds to arrange these into seven groups: Groups. All between— Individu- als. I 21 II M 4- 3d and M + 2d 67 ill M -j- 2d and it -f d 162 IV .. 500 V . 162 VI M — 2d and il — 3d 67 VII M — 3d and M — nd 21 Prof. Porter says: “The mean height, weight, girth of chest, etc., of each of these groups at any age will bo the type of a certain degree of deviation from the mean of the age. That is to say, the weights, etc., of each group will bo symmetrically dis- tributed above and below the mean weight, etc., of the group in the manner illustrated for the entire undivided number of observations, e. g., the entire thousand. Each group, therefore, will be characterized by a physical development definitely determined by the means of height, weight, and other physical dimensions. These means, taken together form the type or norm of the group. The individual deviations from this norm follow the theory of probability, and the degree of abnormality presented by any individual deviation can be expressed in terms of this theory. “For example: A boy H shows deviation in height of + 1.5d from the mean height of his age. He falls, therefore in Group III. The boys of this group possess a mean weight of M kilograms, with a probable deviation of ± d; that is, boys between d and 2d taller than the norm of their age should weigh M ^ cl kilo- grams. In like manner they should have a chest girth of M ^ d inches and a' lung capacity of MJ- d cubic inches, and so on. If the weight and height, etc., of the boy II coincide with the means of his group, his physique is normal; if he devi- ate more than -|- d from the mean in one or more dimensions, his development is abnormal, and the degree of abnormality is measured by the amount of his deviation. “Height, being more stable and less liable to fluctuations than weight, is usually taken as the basis. Excessive weight may be reduced, while height once attained can not be reduced, nor can growth in height be so easily influenced. “By this system the question whether any deviation is normal or abnormal is answered in two ways: In regard to height, by the degree of deviation from the mean or norm of the whole number of observations; in regard of other dimensions, by the degree of deviation of the weight, girth of chest, etc., from the mean weight