An Introduction to the theory of statistics

Bibliographic data

Monograph

Identifikator:: 1751730271

URN:: urn:nbn:de:zbw-retromon-127610

Document type:: Monograph

Author:: Yule, George Udny http://d-nb.info/gnd/12910504X

Title:: An Introduction to the theory of statistics

Edition:: 8. ed. rev

Place of publication:: London

Publisher:: Griffin

Year of publication:: 1927

Scope:: XV, 422 S; Ill., Diagr

Digitisation:: 2021

Collection:: Economics Books

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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part I. The theory of atributes

Collection:: Economics Books

THEORY OF STATISTICS. the mingling of records, e.g. respecting the two sexes, which a careful worker would keep distinct. Take the following case, for example. Suppose there have been 200 patients in a hospital, 100 males and 100 females, suffering from some disease. Suppose, further, that the death-rate for males (the case mortality) has been 30 per cent., for females 60 per cent. A new treatment is tried on 80 per cent. of the males and 40 per cent. of the females, and the results published without distinction of sex. The three attributes, with the relations of which we are here concerned, are death, treatment and male sex. The data show that more males were treated than females, and more females died than males ; therefore the first attribute is associated nega- tively, the second positively, with the third. It follows that there will be an illusory negative association between the first two— death and treatment. If the treatment were completely inefficient we would, in fact, have the following results :— Males. Females. Total. Treated and died . . . 4 24 48 » and did not die . 6 16 72 Not treated and died . : ; 36 42 ry and did not die , i 4 38 v.e. of the treated, only 48/120 =40 per cent. died, while of those not treated 42/80 =0525 per cent. died. If this result were stated without any reference to the fact of the mixture of the sexes, to the different proportions of the two that were treated and to the different déath-rates under normal treatment, then some value in the new treatment would appear to be suggested. To make a fair return, either the results for the two sexes should be stated separately, or the same proportion of the two sexes must receive the experimental treatment. Further, care would have to be taken in such a case to see that there was no selection (perhaps unconscious) of the less severe cases for treat- ment, thus introducing another source of fallacy (deat’ positively associated with severity, treatment negatively associated with severity, giving rise to illusory negative association between treatment and death). A misleading association between the characters of parent and offspring might similarly be created if the records for male-male and female-female lines of descent were mixed. Thus suppose 50 per cent. of males and 10 per cent. of females exhibit some attribute for which there is no association in either line, then we would have for each line and for a mixed record of equal numbers— 50

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