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 167 selection. It will then be necessary in determining the validity of the test to repeat the test and use an average of the two scores. The remedy for errors due to the second factor consists in making the necessary improvements in the test and the pro- cedure used in administering it. The reliability coefficient of a test is raised by increasing the range of ability measured. The relationship between range of test scores and coefficient of reliability is given in the following formula (86, p. 222): ¢ VI=R (1) re ED e— 2 Vi—r In this formula ¢ is the standard deviation of the more re- stricted group and 7 the reliability coefficient obtained with this group, = the standard deviation of the other group and R the reliability coefficient obtained with this group. If a test has an observed reliability coefficient of . 50 when used with a group having a standard deviation of 1, it should yield a reliability coefficient of .87 with a group which has twice as large a standard deviation. The reliability of a test may also be raised by increasing its length. The relationship between the length of a test and its reliability is given by Spearman’s prediction formula, often erroneously called Brown’s formula (86, p. 205): Nrxx, (2) Vipx, = 1+ (—1Dran, Here r.., is the reliability coefficient of a test x, of given length, = the number by which the length of the test is multiplied, and r.,., the reliability of the lengthened test xy, The assumption is made that all of the # parts have the same reliability. Doubling the length of a test having a reliability of .50 increases its reliability to .67. The effect which a change in the length of a test will have upon the correlation of the test with the criterion is shown in the formula at the top of the following page (86, p. 200):

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