Vernon and Straker1 claim that 5·37–9·45 per cent of colour blind men were found in Great Britain, according to district, averaging 7·49 per cent. This is about twice the accepted figure. They suggest the difference is due to use of "a modified form" of the Stilling and Ishihara Tests, which "picks out many of the colour-weak, or anomalous trichromats, as well as the strictly colour-blind".
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NATURE, 152, 690 (1944).
NATURE, 153, 409 (1944).
Edridge Green, F. W., "The Physiology of Vision", chapter 24.
Houstoun, R. A., "Vision and Colour Vision", 194–199.
Cf. Thomas, G. J., Amer. J. Psych., 56, 583.
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PICKFORD, R. The Ishihara Test for Colour Blindness. Nature 153, 656–657 (1944). https://doi.org/10.1038/153656b0
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