Registration of non-melanoma skin cancers in Scotland-how accurate are site and morphology codes?

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Abstract
Although under-reporting of non-melanoma skin cancers to cancer registries is widely acknowledged, less is known about the accuracy of information held about registered cases. In 1993, the accuracy of a random sample of cancer registrations in Scotland attributed to the year 1990 was assessed by reference to relevant medical records. The sample contained 290 registrations of non-melanoma skin cancers, 251 (90%) of which had records available for scrutiny. Here we report the results of a detailed analysis of the accuracy of site and morphology coding of non-melanoma skin cancers. Following reabstraction of details from available medical records, only three cases (1.2%) did not retain the same first three digit ICD-9 site code (173.--), although a further three cases were judged to have been registered in error. There were 56 (21.5%) discrepancies in morphology coding, but 21 of these arose through inferences about morphology in the absence of microscopic confirmation, and most of the remainder were of a relatively minor nature. In summary, it does seem possible to collect data about non-melanoma skin cancers to a reasonably high standard of accuracy. This provides some justification to those who advocate an increased effort directed towards improving levels of completeness of case ascertainment.