The Ishihara Test: on the prevention of job discrimination

Experiments were carried out to answer questions relative to the use of the 24-plate edition of the Ishihara Test for Colour-Blindness as a screening instrument for detecting the presence of inherited color defective vision. Subjects and their numbers varied between some experiments. Some subjects had normal color vision and others had inherited color defectiveness as confirmed with a Nagel anomaloscope. Most of the 157 subjects who participated in the experiments were either young deaf college students or police recruits with normal hearing who did not pass the Ishihara Test during their respective visual screening processes. Some hearing faculty and staff participated as part of Experiment 2. Item analysis and statistics applied to test the significance of differences between group means were applied to derive the following results: (a) test-retest reliability for the Ishihara is high both for persons with inherited color defectiveness and normal color vision; (b) persons making fewer than five errors on the first 13 plates made common incidental (nontypical) errors not related to color defective vision; and (c) five (5) or more errors was identified with some degree of inherited color defective vision, and subsequent referral for additional color vision diagnostics is warranted. Failure to utilize the recommended "pass-fail" criterion and/or to allow clients who fail color vision screening recourse to additional testing to establish type and degree of color defective vision may unnecessarily lead to job discrimination and/or interfere in a negative manner with the career selection process.