To the Editor.—
I fully endorse the need for reliability studies such as comparison by Griffiths et al1 of two methods for assessing cutaneous photodamage, but I am concerned with their interpretation of the findings. In this report, the authors maintain that the photonumeric scale has achieved an acceptable degree of reliability and suggest its wider use. The results of this study, however, suggest that both methods tested are anything but reliable: to a reader with limited knowledge of the k statistic,2 k=.31 for the photonumeric scale compared with k=.11 for the descriptive method may sound impressive, especially when the difference between the two is found to be highly statistically significant (P<.0001). Readers should note, however, that k=.31 essentially implies that the between-observer agreement was only 31% better than could be expected by chance alone. The study has been useful in showing us that both measures are
Williams HC. A Photonumeric Scale for the Assessment of Cutaneous Photodamage. Arch Dermatol. 1992;128(10):1406–1407. doi:10.1001/archderm.1992.01680200118026
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