Procedures in employment psychology

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Monograph

Identifikator:: 173623112X

URN:: urn:nbn:de:zbw-retromon-112923

Document type:: Monograph

Author:: Bingham, Walter Van Dyke http://d-nb.info/gnd/123042593; Freyd, Max

Title:: Procedures in employment psychology

Place of publication:: Chicago & New York

Publisher:: Shaw

Year of publication:: 1926

Scope:: XI, 269 S

Digitisation:: 2020

Collection:: Economics Books

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Document type:: Monograph

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Title:: XIII. Validation of the measuring instruments

Collection:: Economics Books

VALIDATION OF MEASURING INSTRUMENTS 171 N the number of cases. The standard deviation or standard error of the difference in means is obtained by the following formula: (8) €="V Om, tox Here om and go, are the standard deviations of the two means. These formulas are not reliable where is less than 2 5. The differentiating value of the test is determined by com- paring the difference in means of the successes and failures with the standard error of this difference. If the difference is twice as great as its error, the chances are 43 in 44 that the difference is real and in the direction indicated; if it is three times as great, the chances are 740 in 741. This state- ment of probability is derived from the normal surface of error. If, for instance, the difference in means is three times as great as its standard error, then on one side of the normal surface of error at a distance from the mean equal to three times the standard deviation, the difference will become zero and beyond that point the values will be reversed; that is, the mean which was formerly the greater will now be the lesser. Since in the normal surface of error 1/ 741 of the measures occur beyond 3 at one side of the curve, we conclude that the chances are 1 in 741 that the difference is not real and not in the direction indicated, or 740 in 741 that it is real and in the direction indicated. A good example of the use of this method is to be found in Fernald, Hayes, and Dawley (51) and Dewey, Child, and Ruml (44) (see Table 8). For practical purposes the investigator may consider a test to be significant if the difference in means of the suc- cesses and failures is two or more times as great as its stand- ard error. A different formula is used when a group is compared with a sub-group; for example, when good, fair, and poor workers combined are compared as a whole with one of these three sub-groups. The formula for the standard deviation of the difference

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