Introduction to medical biometry and statistics / by Raymond Pearl.

  • Raymond Pearl
Date:
1930
Catalogue details

Licence: In copyright

Credit: Introduction to medical biometry and statistics / by Raymond Pearl. Source: Wellcome Collection.

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    Such a count furnishes us at once with a great deal of per- fectly definite and precise information about this group or popula- tion of balls. For example, the count tells us that it will never be possible to take away from the basket more than one pair of balls of which one member is green. This is a definite attribute of this population which may be used to differentiate it from other popula- tions. In this particular population only one green ball occurs. This sort of knowledge derived by counting is perfectly definite and precise so far as relates to the particular group which it con- cerns in any particular case. It does not involve any approxima- tion, or probability, and is as precise as knowledge of the indi- vidual. It, however, pertains to the group. It forms a part of a proper scientific description of a group to count the numbers of each of the different kinds of elements which compose it. 2. Knowledge of certain abstract qualities of groups. This knowledge is obtained by calculation from the data got by counting. The more important of the abstract qualities* of groups are: (a) The central or typical condition of the group; or the condi- tion about which the individuals composing the group cluster. This is variously measured: by the arithmetic mean or average, which gives the center of gravity of the group; by the median, which tells the point on either side of which exactly half the individuals fall; by the mode, which tells the point of greatest frequency of occurrence in the group, etc. (.b) The degree of individual diversity comprised in the group. This attribute, called the variability of the group, is again variously measured: by standard deviations, coefficients of variation, etc. (c) The degree of asymmetry of the distribution of the indi- viduals composing the group. This is measured by the skewness or other related constants. (d) Various other attributes of distributions might be here included, such as, for example, the kurtosis, but for purposes of the present general analysis this is not necessary. Though some of these attributes involve very complex mathematical expressions for their determination, the general fact remains clear that they are * A more detailed discussion of the following constants will be found in Chapter XIII.
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