Pass rates for the Farnsworth D15 colour vision test.

INTRODUCTION: The Farnsworth D15 test (D15) is used worldwide to select applicants for employment in occupations which require good colour vision. People with slight colour deficiency are intended to pass the D15 and people with significant (moderate/severe) colour deficiency to fail.
METHODS: Pass rates were determined for 710 adult males with red-green colour deficiency using three different pass criteria in general use.
RESULTS: Forty-six per cent of subjects were successful when the pass criterion was a circular results diagram (one single transformation of adjacent hues was accepted as a pass), 53% passed when one red-green isochromatic error was allowed and 60% passed when two red-green isochromatic errors were permitted. The pass rate for 200 dichromats was 1.5% on a circular diagram, 3% on one red-green error and 6% on two red-green errors. Protans made fewer errors than deutans and more protans than deutans were successful when either one or two red-green crossings were permitted as a pass.
CONCLUSION: A circular results diagram is the preferred pass criterion. This criterion most nearly fulfils the aim of the test to fail all dichromats and people with significant protanomalous and deuteranomalous trichromatism. A circular diagram is also easy to interpret consistently. Re-examination is recommended if there are only one or two red-green isochromatic error lines across the results diagram. This gives individuals with borderline slight/moderate colour deficiency an opportunity to pass at the second attempt.