What is an evidence code?

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Every annotation must be attributed to a source, which may be a literature reference, another database or a computational analysis. The annotation must indicate what kind of evidence is found in the cited source to support the association between the gene product and the GO term. A simple controlled vocabulary is used to record evidence; and the evidence codes are simply the three-letter codes used to signify the type of evidence cited. More information on the meaning and use of the evidence codes can be found in the GO evidence codes documentation.